of 


FRAGMENTS  OF  SCIENCE 


FOR 


UNSCIENTIFIC  PEOPLE: 


A  SERIES  OF  DETACHED  ESSAYS,  LECTURES, 
AND  REVIEWS. 


BY 
JOHN  TYNDALL,   LL.  D.,  F.  R.  S., 

ATITIIOE  OF  "HEAT  AS  A  •"*••*•«•  OF,  MfflifTTr."  "T-""~^"^"  ON  SOUKD,"  ETC.,  ETC. 


ORK: 
D.     APPLETON    AND    COMPANY, 

549   &   551   BROADWAY. 

1871. 


PEEFACE. 


MY  MOTIVE  in  writing  these  papers  was  mainly  that 
which  prompted  the  publication  of  my  Royal  Institu- 
tion lectures  ;  a  desire,  namely,  to  extend  sympathy  for 
science  beyond  the  limits  of  the  scientific  public. 

The  fulfilment  of  this  desire  has  caused  a  tempo- 
rary and  sometimes  reluctant  deflection  of  thought 
from  the  line  of  original  research.  But  considering 
the  result  aimed  at,  and  in  part  I  trust  achieved,  I  do 
not  regret  the  price  paid  for  it. 

I  have  carefully  looked  over  all  the  articles  here 
printed,  added  a  little,  omitted  a  little — in  fact,  tried 
as  far  as  my  time  permitted  to  render  the  work  pre- 
sentable. Most  of  the  essays  are  of  a  purely  scien- 
tific character,  and  from  those  which  are  not,  I  have 
endeavored,  without  veiling  my  convictions,  to  exclude 
every  word  that  could  cause  needless  irritation. 

From  America  the  impulse  came  which  induced  me 
to  gather  these  "  Fragments "  together,  and  to  my 
friends  in  the  United  States  I  dedicate  them. 

JOHN  TYNDALL. 

ATHEN.EUM  CLUB  :  March,  1871. 


CONTENTS. 


I. — THE  CONSTITUTION  OF  NATURE,        .            .  1 

II. — THOUGHTS  ON  PRAYER  AND  NATURAL  LAW,       .            .  33 

III. — MIRACLES  AND  SPECIAL  PROVIDENCES,           .            .     ,  .43 

^    IV.— MATTER  AND  FORCE,        .            .            .            .            .  71 

V. — AN  ADDRESS  TO  STUDENTS,  .              .            .            .  .95 

VI. — SCOPE  AND  LIMIT  OF  SCIENTIFIC  MATERIALISM,               .  107 

x  VII. — SCIENTIFIC  USE  OF  THE  IMAGINATION,          .            .  .125 

VIII.— ON  RADIATION,                .....  1C7 

IX. — ON  RADIANT  HEAT  IN  RELATION  TO  THE  COLOR  AND  CHEMI- 
CAL CONSTITUTION  OF  BODIES,               .            .  .211 
1L — ON  CHEMICAL  RATS   AND  THE  STRUCTURE   AND  LIGHT  OF 

THE  SKY,           .            .            .            .            .  .235 

XI. — DUST  AND  DISEASE,        .....  275 

ADDITION  TO  "DUST  AND  DISEASE,"    .            .  .       323 

XII.— LIFE  AND  LETTERS  OF  FARADAY,            .            .            .  329 

XIII. — AN  ELEMENTARY  LECTURE  ON  MAGNETISM,             .  .       353 
XIV. — SHORTER  ARTICLES  : 

SLATES, 377 

DEATH  BY  LIGHTNING,  ....       397 

SCIENCE  AND  SPIRITS,           ....  402 

VITALITY,          .            .            .            .            .  .      410 

ADDITIONAL  REMARKS  ON  MIRACLES,            .  418 


I. 

THE  CONSTITUTION  OF  NATURE. 

AN    ESSAY. 
[Fortnightly  Review,  vol.  iii.  p.  129.] 


"  The  gentle  Mother  of  all 
Showed  me  the  lore  of  colors  and  of  sounds  ; 
The  innumerable  tenements  of  beauty  ; 
The  miracle  of  generative  force  ; 
Far-reaching  concords  of  Astronomy 
Felt  in  the  plants  and  in  the  punctual  birds  ; 
Mainly,  the  linked  purpose  of  the  whole ; 
And,  chiefest  prize,  found  I  true  liberty — 
The  home  of  homes  plain-dealing  Nature  gave." 

RALPH  WALDO  EMERSON. 


I. 

THE  CONSTITUTION  OF  NATURE. 

WE  cannot  think  of  space  as  finite,  for  wherever  in 
imagination  we  erect  a  boundary  we  are  compelled  to  think 
of  space  as  existing  beyond  that  boundary.  Thus  by  the 
incessant  dissolution  of  limits  we  arrive  at  a  more  or  less 
adequate  idea  of  the  infinity  of  space.  But  though  com- 
pelled to  think  of  space  as  unbounded,  there  is  no  mental 
necessity  to  compel  us  to  think  of  it  either  as  filled  or  as 
empty ;  whether  it  is  filled  or  empty  must  be  decided  by 
experiment  and  observation.  That  it  is  not  entirely  void, 
the  starry  heavens  declare ;  but  the  question  still  remains, 
Are  the  stars  themselves  hung  in  vacuof  Are  the  vast 
regions  which  surround  them,  and  across  which  their  light 
is  propagated,  absolutely  empty  ?  A  century  ago  the 
answer  to  this  question  would  be,  "  No,  for  particles  of 
light  are  incessantly  shot  through  space."  The  reply  of 
modern  science  is  also  negative,  but  on  a  somewhat  differ- 
ent ground.  It  has  the  best  possible  reasons  for  rejecting 
the  idea  of  luminiferous  particles ;  but,  in  support  of  the 
conclusion  that  the  celestial  spaces  are  occupied  by  matter, 
it  is  able  to  offer  proofs  almost  as  cogent  as  those  which 
can  be  adduced  for  the  existence  of  an  atmosphere  round 
the  earth.  Men's  minds,  indeed,  rose  to  a  conception  of 
the  celestial  and  universal  atmosphere  through  the  study 
of  the  terrestrial  and  local  one.  Frqm  the  phenomena  of 
sound  as  displayed  in  the  air,  they  ascended  to  the  phe~ 


10  FRAGMENTS  OF  SCIENCE. 

nomena  of  light  as  displayed  in  the  ether  /   which  is  the 
name  given  to  the  interstellar  medium. 

x  The  notion  of  this  medium  must  not  be  considered  as 
\  a  vague  or  fanciful  conception  on  the  part  of  scientific  men. 
Of  its  reality  most  of  them  are  as  convinced  as  they  are  of 
the  existence  of  the  sun  and  moon.  The  luminiferous  ether 
has  definite  mechanical  properties.  It  is  almost  infinitely 
more  attenuated  than  any  known  gas,  but  its  properties  are 
those  of  a  solid  rather  than  of  a  gas.  It  resembles  jelly 
rather  than  air.  A  body  thus  constituted  may  have  its 
boundaries ;  but,  although  the  ether  may  not  be  coexten- 
sive with  space,  we  at  all  events  know  that  it  extends  as 
far  as  the  most  distant  visible  stars.  In  fact,  it  is  the  ve- 
hicle of  their  light,  and  without  it  they  could  not  be  seen. 
This  all-pervading  substance  takes  up  their  molecular  tre- 
mors, and  conveys  them  with  inconceivable  rapidity  to  our  or- 
gans of  vision.  It  is  the  transported  shiver  of  bodies  count- 
less millions  of  miles  distant,  which  translates  itself  in  human 
consciousness  into  the  splendor  of  the  firmament  at  night. 

If  the  ether  have  a  boundary,  masses  of  ponderable 
matter  might  be  conceived  to  exist  beyond  it,  but  they 
could  emit  no  light.  Beyond  the  ether  dark  suns  might 
burn  ;  there,  under  proper  conditions,  combustion  might  be 
carried  on ;  fuel  might  consume  unseen,  and  metals  be 
heated  to  fusion  in  invisible  fires.  A  body,  moreover,  once 
heated  there,  would  continue  forever  heated ;  a  sun  or 
planet,  once  molten,  would  continue  forever  molten.  For, 
the  loss  of  heat  being  simply  the  abstraction  of  molecular 
motion  by  the  ether,  where  this  medium  is  absent  no  cool- 
ing could  occur.  A  sentient  being,  on  approaching  a  heated 
body  in  this  region,  would  be  conscious  of  no  augmentation 
of  temperature.  The  gradations  of  warmth  dependent  on 
the  laws  of  radiation  would  not  exist,  and  actual  contact 
would  first  reveal  the  heat  of  an  extra  ethereal  sun. 

Imagine  a  paddle-wheel  placed  in  water  and  caused  to 


THE   CONSTITUTION   OF  NATURE.  11 

rotate.  From  it,  as  a  centre,  waves  would  issue  in  all 
directions,  and  a  wader,  as  he  approached  the  place  of  dis- 
turbance, would  be  met  by  stronger  and  stronger  waves. 
This  gradual  augmentation  of  the  impressions  made  upon 
the  wader's  body  is  exactly  analogous  to  the  augmentation 
of  light  when  we  approach  a  luminous  source.  In  the  one 
case,  however,  the  coarse  common  nerves  of  the  body  suf- 
fice ;  for  the  other  we  must  have  the  finer  optic  nerve.  But 
suppose  the  water  withdrawn;  the  action  at  a  distance 
would  then  cease,  and,  as  far  as  the  sense  of  touch  is  con- 
cerned, the  wader  would  be  first  rendered  conscious  of  the 
motion  of  the  wheel  by  the  actual  blow  of  the  paddles. 
The  transference  of  motion  from  the  paddles  to  the  water 
is  mechanically  similar  to  the  transference  of  molecular 
motion  from  the  heated  body  to  the  ether  ;  and  the  propa- 
gation of  waves  through  the  liquid  is  mechanically  similar 
to  the  propagation  of  light  and  radiant  heat. 

As  far  as  our  knowledge  of  space  extends,  we  are  to 
conceive  it  as  the  holder  of  the  luminiferous  ether,  through 
which  are  interspersed,  at  enormous  distances  apart,  the 
ponderous  nuclei  of  the  stars.  Associated  with  the  star 
that  most  concerns  us  we  have  a  group  of  dark  planetary 
masses  revolving  at  various  distances  round  it,  each  again 
rotating  on  its  own  axis  ;  and,  finally,  associated  with  some 
of  these  planets  we  have  dark  bodies  of  minor  note — the 
moons.  Whether  the  other  fixed  stars  have  similar  plane- 
tary companions  or  not  is  to  us  a  matter  of  pure  conjecture, 
which  may  or  may  not  enter  into  our  conception  of  the 
universe.  But,  probably,  every  thoughtful  person  believes, 
with  regard  to  those  distant  suns,  that  there  is  in  space 
something  besides  our  system  on  which  they  shine. 

Having  thus  obtained  a  general  view  of  the  present 
condition  of  space,  and  of  the  bodies  contained  in  it,  we 
may  inquire  whether  things  were  so  created  at  the  begin- 
ning. Was  space  furnished  at  once,  "by  the  fiat  of  Omnipo- 


12  FRAGMENTS  OF  SCIENCE. 

tcnce,  with  these  burning  orbs  ?  To  this  question  the  man 
of  science,  if  he  confine  himself  within  his  own  limits,  will 
give  no  answer,  though  it  must  be  remarked  that  in  the 
formation  of  an  opinion  he  has  better  materials  to  guide 
him  than  anybody  else.  He  can  clearly  show,  however, 
that  the  present  state  of  things  may  be  derivative.  He 
can  even  assign  reasons  which  render  probable  its  deriva- 
tive origin — that  it  was  not  originally  what  it  now  is.  At 
all  events,  he  can  prove  that  out  of  common  non-luminous 
matter  this  whole  pomp  of  stars  might  have  been  evolved. 

The  law  of  gravitation  enunciated  by  Newton  is,  that 
every  particle  of  matter  in  the  universe  attracts  every  other 
particle  with  a  force  which  diminishes  as  the  square  of  the 
distance  increases.  Thus  the  sun  and  the  earth  mutually 
pull  each  other ;  thus  the  earth  and  the  moon  are  kept  in 
company ;  the  force  which  holds  every  respective  pair  of 
masses  together  being  the  integrated  force  of  their  com- 
ponent parts.  Under  the  operation  of  this  force,  a  stone 
falls  to  the  ground  and  is  warmed  by  the  shock ;  under  its 
operation  meteors  plunge  into  our  atmosphere  and  rise  to 
incandescence.  Showers  of  such  doubtless  fall  incessantly 
upon  the  sun.  Acted  on  by  this  force,  were  it  stopped  in 
its  orbit  to-morrow7,  the  earth  would  rush  toward,  and  finally 
combine  with,  the  sun.  Heat  would  also  be  developed  by 
this  collision,  and  Mayer,  Helmholtz,  and  Thomson,  have 
calculated  its  amount.  It  would  equal  that  produced  by 
the  combustion  of  more  than  five  thousand  worlds  of  solid 
coal,  all  this  heat  being  generated  at  the  instant  of  collision. 
In  the  attraction  of  gravity,  therefore,  acting  upon  non- 
luminous  matter,  we  have  a  source  of  heat  more  powerful 
than  could  be  derived  from  any  terrestrial  combustion.  And 
were  the  matter  of  the  universe  cast  in  cold  detached  frag- 
ments into  space,  and  there  abandoned  to  the  mutual  gravi- 
tation of  its  own  parts,  the  collision  of  the  fragments  would 
in  the  end  produce  the  fires  of  the  stars. 


THE   CONSTITUTION   OF  NATURE.  13 

The  action  of  gravity  upon  matter  originally  cold  may, 
in  fact,  be  the  origin  of  all  light  and  heat,  and  the  proxi- 
mate source  of  such  other  powers  as  are  generated  by 
light  and  heat.  But  we  have  now  to  inquire  what  is  the 
light  and  what  is  the  heat  thus  produced  ?  This  question 
has  already  been  answered  in  a  general  way.  Both  light 
and  heat  are  modes  of  motion.  Two  planets  clash  and 
come  to  rest;  their  motion,  considered  as  masses,  is  de- 
stroyed, but  it  is  really  continued  as  a  motion  of  their 
ultimate  particles.  It  is  this  motion,  taken  up  by  the 
ether,  and  propagated  through  it  with  a  velocity  of  one 
hundred  and  eighty-five  thousand  miles  a  second,  that  comes 
to  us  as  the  light  and  heat  of  suns  and  stars.  The  atoms 
of  a  hot  body  swing  with  inconceivable  rapidity,  but  this 
power  of  vibration  necessarily  implies  the  operation  of 
forces  between  the  atoms  themselves.  It  reveals  to  us 
that,  while  they  are  held  together  by  one  force,  they  are 
kept  asunder  by  another,  their  position  at  any  moment  de- 
pending on  the  equilibrium  of  attraction  and  repulsion.  The 
atoms  are  virtually  connected  by  elastic  springs,  which  op- 
pose at  the  same  time  their  approach  and  their  retreat,  but 
which  tolerate  the  vibration  called  heat.  When  two  bod- 
ies drawn  together  by  the  force  of  gravity  strike  each  other, 
the  intensity  of  the  ultimate  vibration,  or,  in  other  words, 
the  amount  of  heat  generated,  is  proportional  to  the  vis 
viva  destroyed  by  the  collision.  The  molecular  motion 
once  set  up  is  instantly  shared  with  the  ether,  and  diffused 
by  it  throughout  space. 

We  on  the  earth's  surface  live  night  and  day  in  the 
midst  of  ethereal  commotion.  The  medium  is  never  still. 
The  cloud-canopy  above  us  may  be  thick  enough  to  shut 
out  the  light  of  the  stars,  but  this  canopy  is  itself  a  warm 
body,  which  radiates  its  motion  through  the  ether.  The 
earth  also  is  warm,  and  sends  its  heat-pulses  incessantly 
forth.  It  is  the  waste  of  its  molecular  motion  in  space 


14  FRAGMENTS   OF  SCIENCE. 

that  chills  the  earth  upon  a  clear  night ;  it  is  the  return 
of  its  motion  from  the  clouds  which  prevents  the  earth's 
temperature  on  a  cloudy  night  from  falling  so  low.  To  the 
conception  of  space  being  filled,  we  must  therefore  add 
the  conception  of  its  being  in  a  state  of  incessant  tremor. 
The  sources  of  vibration  are  the  ponderable  masses  of  the 
universe.  Let  us  take  a  sample  of  these  and  examine  it  in 
detail.  When  we  look  to  our  planet  we  find  it  to  be  an 
aggregate  of  solids,  liquids,  and  gases.  When  we  look  at 
any  one  of  these,  we  generally  find  it  composed  of  still 
more  elementary  parts.  We  learn,  for  example,  that  the 
water  of  our  rivers  is  formed  by  the  union,  in  definite  pro- 
portions, of  two  gases,  oxygen  and  hydrogen.  We  know 
how  to  bring  these  constituents  together,  and  to  cause  them 
to  form  water :  we  also  know  how  to  analyze  the  water, 
and  recover  from  it  its  two  constituents.  So,  likewise,  as 
regards  the  solid  proportions  of  the  earth.  Our  chalk-hills, 
for  example,  are  formed  by  a  combination  of  carbon,  oxy- 
gen, and  calcium.  These  are  elements  the  union  of  which, 
in  definite  proportions,  has  resulted  in  the  formation  of 
chalk.  The  flints  within  the  chalk  we  know  to  be  a  com- 
pound of  oxygen  and  silicium,  called  silica ;  and  our  or- 
dinary clay  is,  for  the  most  part,  formed  by  the  union  of 
silicium,  oxygen,  and  the  well-known  light  metal,  alumin- 
ium. By  far  the  greater  portion  of  the  earth's  crust  is 
compounded  of  the  elementary  substances  mentioned  in 
these  few  lines. 

The  principle  of  gravitation  has  been  already  described 
as  an  attraction  which  every  particle  of  matter,  however 
small,  has  for  every  other  particle.  With  gravity  there  is 
no  selection ;  no  particular  atoms  choose,  by  preference, 
other  particular  atoms  as  objects  of  attraction  ;  the  attrac- 
tion of  gravitation  is  proportional  to  the  quantity  of  the 
attracting  matter,  regardless  of  its  quality.  But  in  the 
molecular  world  which  we  have  now  entered  matters  are 


THE   CONSTITUTION   OF  NATURE.  15 

otherwise  arranged.  Here  we  have  atoms  between  which 
a  strong  attraction  is  exercised,  and  also  atoms  between 
which  a  weak  attraction  is  exercised.  One  atom  can  jostle 
another  out  of  its  place  in  virtue  of  a  superior  force  of  at- 
traction. But  though  the  amount  of  force  exerted  varies 
thus  from  atom  to  atom,  it  is  still  an  attraction  of  the  same 
mechanical  quality,  if  I  may  use  the  term,  as  that  of  grav- 
ity itself.  Its  intensity  might  be  measured  in  the  same 
way,  namely,  by  the  amount  of  motion  which  it  can  impart 
in  a  certain  time.  Thus  the  attraction  of  gravity  at  the 
earth's  surface  is  expressed  by  the  number  thirty-two,  be- 
cause, when  acting  freely  on  a  body  for  a  second  of  time, 
it  imparts  to  the  body  a  velocity  of  thirty-two  feet  a  second. 
In  like  manner  the  mutual  attraction  of  oxygen  and  hydro- 
gen might  be  measured  by  the  velocity  imparted  to  the 
atoms  in  their  rushing  together.  Of  course  such  a  unit  of 
time  as  a  second  is  not  here  to  be  thought  of,  the  whole 
interval  required  by  the  atoms  to  cross  the  minute  spaces 
which  separate  them  not  amounting  probably  to  more  than 
an  inconceivably  small  fraction  of  a  second. 

It  has  been  stated  that  when  a  body  falls  to  the  earth 
it  is  warmed  by  the  shock.  Here  we  have  what  we  may 
call  a  mechanical  combination  of  the  earth  and  the  body. 
Suffer  the  falling  body  and  the  earth  to  dwindle  in  imagi- 
nation to  the  size  of  atoms,  and  for  the  attraction  of  grav- 
ity substitute  that  of  chemical  affinity,  which  is  the  name 
given  to  the  molecular  attraction,  we  have  then  what  is 
called  a  chemical  combination.  The  effect  of  the  union  in 
this  case  also  is  the  development  of  heat,  and  from  the 
amount  of  heat  generated  we  can  infer  the  intensity  of  the 
atomic  pull.  Measured  by  ordinary  mechanical  standards, 
this  is  enormous.  Mix  eight  pounds  of  oxygen  with  one 
of  hydrogen,  and  pass  a  spark  through  the  mixture ;  the 
gases  instantly  combine,  their  atoms  rushing  over  the  little 
distances  between  them.  Take  a  weight  of  forty-seven 


16  FRAGMENTS  OF  SCIENCE. 

thousand  pounds  to  an  elevation  of  one  thousand  feet  above 
the  earth's  surface,  and  let  it  fall ;  the  energy  with  which 
it  would  strike  the  earth  would  not  exceed  that  of  the  eight 
pounds  of  oxygen  atoms  as  they  dash  against  one  pound 
of  hydrogen  atoms  to  form  water. 

It  is  sometimes  stated  that  the  force  of  gravity  is  dis- 
tinguished from  all  other  forces  by  the  fact  of  its  resisting 
conversion  into  any  other.  Chemical  affinity,  it  is  said, 
can  be  converted  into  heat  and  light,  and  these  again  into 
magnetism  and  electricity.  But  gravity  refuses  to  be  so 
converted ;  it  is  a  force  which  maintains  itself  under  all 
circumstances,  and  is  not  capable  of  disappearing  to  give 
place  to  another.  If  by  this  is  meant  that  a  particle  of 
matter  can  never  be  deprived  of  its  weight,  the  assertion 
is  correct ;  but  the  law  which  affirms  the  convertibility  of 
natural  forces  was  never  meant,  in  the  minds  of  those  who 
understood  it,  to  affirm  that  such  a  conversion  as  that  here 
implied  occurs  in  any  case  whatever.  As  regards  converti- 
bility into  heat,  gravity  and  chemical  affinity  stand  on  pre- 
cisely the  same  footing.  The  attraction  in  the  one  case  is 
as  indestructible  as  in  the  other.  Nobody  affirms  that 
when  a  stone  rests  upon  the  surface  of  the  earth  the  mutual 
attraction  of  the  earth  and  stone  is  abolished ;  nobody 
means  to  affirm  that  the  mutual  attraction  oi  oxygen  for 
hydrogen  ceases  after  the  atoms  have  combined  to  form 
water.  What  is  meant  in  the  case  of  chemical  affinity  is, 
that  the  pull  of  that  affinity,  acting  through  a  certain  space, 
imparts  a  motion  of  translation  of  the  one  atom  toward  the 
other.  This  motion  of  translation  is  not  heat,  nor  is  the 
force  that  produces  it  heat.  But  when  the  atoms  strike  and 
recoil,  the  motion  of  translation  is  converted  into  a  motion 
of  vibration,  and  this  latter  motion  is  heat.  But  the  vibra- 
tion, so  far  from  causing  the  extinction  of  the  original  at- 
traction, is  in  part  carried  on  by  that  attraction.  The  atoms 
recoil  in  virtue  of  the  elastic  force  which  opposes  actual 


THE   CONSTITUTION   OF  NATURE.  17 

contact,  and  in  the  recoil  they  are  driven  too  far  back.  The 
original  attraction  then  triumphs  over  the  force  of  recoil, 
and  urges  the  atoms  once  more  together.  Thus,  like  a  pen- 
dulum, they  oscillate,  until  their  motion  is  imparted  to  the 
surrounding  ether ;  or,  in  other  words,  until  their  heat  be- 
comes radiant  heat. 

In  this  sense,  and  in  this  sense  only,  is  chemical  affinity 
converted  into  heat.  There  is,  first  of  all,  the  attraction 
between  the  atoms  ;  there  is,  secondly,  space  between  them. 
Across  this  space  the  attraction  urges  them.  They  collide, 
they  recoil,  they  oscillate.  There  is  a  change  in  the  form 
of  the  motion,  but  there  is  no  real  loss.  It  is  so  with  the 
attraction  of  gravity.  To  produce  motion  here,  space  must 
also  intervene  between  the  attracting  bodies :  when  they 
strike  motion  is  apparently  destroyed,  but  in  reality  there 
is  no  destruction.  Their  atoms  are  suddenly  urged  together 
by  the  shock ;  by  their  own  perfect  elasticity  these  atoms 
recoil ;  and  thus  is  set  up  the  molecular  oscillation  which 
announces  itself  to  the  nerves  as  heat. 

It  was  formerly  universally  supposed  that  by  the  colli- 
sion of  unelastic  bodies  force  was  destroyed.  Men  saw,  for 
example,  when  two  spheres  of  clay,  or  painter's  putty,  or 
lead,  were  urged  together,  that  the  motion  possessed  by 
the  masses  prior  to  impact  was  more  or  less  annihilated. 
They  believed  in  an  absolute  destruction  of  the  force  of 
impact.  Until  recent  times,  indeed,  no  difficulty  was  ex- 
perienced in  believing  this,  whereas,  at  present,  the  ideas 
of  force  and  its  destruction  refuse  to  be  united  in  most 
philosophic  minds.  In  the  collision  of  elastic  bodies,  on  the 
contrary,  it  was  observed  that  the  motion  with  which  they 
clashed  together  was  in  great  part  restored  by  the  resiliency 
of  the  masses,  the  more  perfect  the  elasticity  the  more  com- 
plete being  the  restitution.  This  led  to  the  idea  of  perfectly 
elastic  bodies — bodies  competent  to  restore  by  their  recoil 
the  whole  of  the  motion  which  they  possessed  before  impact. 


18  FRAGMENTS  OF  SCIENCE. 

Hence  the  idea  of  the  conservation  of  force,  as  opposed 
to  the  destruction  of  force,  which  was  supposed  to  occur 
when  inelastic  bodies  met  in  collision. 

We  now  know  that  the  principle  of  conservation  holds 
equally  good  with  elastic  and  unelastic  bodies.  Perfectly 
elastic  bodies  develop  no  heat  on  collision.  They  retain 
their  motion  afterward,  though  its  direction  may  be  changed ; 
and  it  is  only  when  sensible  motion  is,  in  whole  or  in  part, 
destroyed  that  heat  is  generated.  This  always  occurs  in 
unelastic  collision,  the  heat  developed  being  the  exact 
equivalent  of  the  motion  extinguished.  This  heat  virtually 
declares  that  the  property  of  elasticity,  denied  to  the  masses, 
exists  among  their  atoms,  and  by  their  recoil  and  oscillation 
the  principle  of  conservation  is  vindicated. 

But  ambiguity  in  the  use  of  the  term  "  force  "  has  been 
for  some  time  more  and  more  creeping  upon  us.  We  called 
the  attraction  of  gravity  a  force  without  any  reference  to 
motion.  A  body  resting  on  a  shelf  is  as  much  pulled  by 
gravity  as  when  after  having  been  pushed  off  the  shelf  it 
falls  toward  the  earth.  We  applied  the  term  force  also  to 
that  molecular  attraction  which  we  called  chemical  affinity. 
When,  however,  we  spoke  of  the  conservation  of  force  in 
the  case  of  elastic  collision,  we  meant  neither  a  pull  nor  a 
push,  which,  as  just  indicated,  might  be  exerted  upon  inert 
matter,  but  we  meant  the  moving  force,  if  I  may  use  the 
term,  of  the  colliding  masses. 

What  I  have  called  moving  force  has  a  definite  me- 
chanical measure  in  the  amount  of  work  that  it  can  perform. 
The  simplest  form  of  work  is  the  raising  of  a  weight.  A 
man  walking  up-hill  or  up-stairs  with  a  pound  weight  in 
his  hand,  to  an  elevation  say  of  sixteen  feet,  performs  a  cer- 
tain amount  of  work  over  and  above  the  lifting  of  his  own 
body.  If  he  ascend  to  a  height  of  thirty-two  feet,  he  does 
twice  the  work ;  if  to  a  height  of  forty-eight  feet,  he  does 
throe  times  the  work ;  if  to  sixty-four  feet,  he  does  four 


THE  CONSTITUTION  OF  NATURE.  19 

times  the  work,  and  so  on.  If,  moreover,  he  carries  up  two 
pounds  instead  of  one,  other  things  being  equal,  he  does 
twice  the  work ;  if  three,  four,  or  five  pounds,  he  does  three, 
four,  or  five  times  the  work.  In  fact,  it  is  plain  that  the 
work  performed  depends  on  two  factors,  the  weight  raised 
and  the  height  to  which  it  is  raised.  It  is  expressed  by  the 
product  of  these  two  factors. 

But  a  body  may  be  caused  to  reach  a  certain  elevation 
in  opposition  to  the  force  of  gravity,  without  being  actually 
carried  up  to  the  elevation.  If  a  hodman,  for  example, 
wished  to  land  a  brick  at  an  elevation  of  sixteen  feet  above 
the  place  where  he  stands,  he  would  probably  pitch  it  up  to 
the  bricklayer.  He  would  thus  impart,  by  a  sudden  effort, 
a  velocity  to  the  brick  sufficient  to  raise  it  to  the  required 
height;  the  work  accomplished  by  that  effort  being  pre- 
cisely the  same  as  if  he  had  slowly  carried  up  the  brick. 
The  initial  velocity  which  must  be  imparted  in  the  case  here 
assumed,  is  well  known.  To  reach  a  height  of  sixteen  feet, 
the  brick  must  quit  the  man's  hand  with  a  velocity  of 
thirty-two  feet  a  second.  It  is  needless  to  say  that  a  body 
starting  with  any  velocity,  would,  if  wholly  unopposed  or 
unaided,  continue  to  move  forever  with  the  same  velocity. 
But  when,  in  the  case  before  us,  the  body  is  thrown  upward, 
it  moves  in  opposition  to  gravity,  which  incessantly  retards 
its  motion,  and  finally  brings  it  to  rest  at  an  elevation  of 
sixteen  feet.  If  not  here  caught  by  the  bricklayer,  it  would 
return  to  the  hodman  with  an  accelerated  motion,  and 
reach  his  hand  with  the  precise  velocity  it  possessed  on 
quitting  it. 

Supposing  the  man  competent  to  impart  to  the  brick,  at 
starting,  a  speed  of  sixty-four  feet  a  second,  or  twice  its 
former  speed,  would  the  amount  of  work  performed  in  this 
effort  be  only  twice  what  it  was  in  the  first  instance  ?  No ; 
it  would  be  four  times  that  quantity.  A  body  starting  with 
twice  the  velocity  of  another,  will  rise  to  four  times  the 


20  FRAGMENTS  OF  SCIENCE. 

height;  in  like  manner,  a  threefold  velocity  will  give  a 
ninefold  elevation,  a  fourfold  velocity  will  give  a  sixteen- 
fold  elevation,  and  so  on.  The  height  attained,  then,  or  the 
work  done,  is  not  proportional  to  the  velocity,  but  to  the 
square  of  the  velocity.  As  before,  the  work  is  also  pro- 
portional to  the  weight  elevated.  Hence  the  work  which 
any  moving  masses  whatever  are  competent  to  perform,,  by 
the  motion  which  they  at  any  moment  possess,  is  jointly 
proportional  to  the  weight  and  the  square  of  the  velocity. 
Here,  then,  we  have  a  second  measure  of  work,  in  which  we 
simply  translate  the  idea  of  height  into  its  equivalent  idea 
of  motion. 

In  mechanics,  the  product  of  the  mass  of  a  moving  body 
into  the  square  of  its  velocity,  expresses  what  is  called  the 
vis  viva,  or  living  force.  It  is  also  sometimes  called  the 
"mechanical  effect."  If,  for  example,  we  point  a  cannon 
upward,  and  start  a  ball  with  twice  the  velocity  imparted 
by  a  second  cannon,  the  ball  will  rise  to  four  times  the 
height.  The  speedier  ball,  if  directed  against  a  target,  will 
also  do  four  times  the  execution.  Hence  the  importance 
of  imparting  a  high  velocity  to  projectiles  in  war.  Having 
thus  cleared  our  way  to  a  perfectly  clear  conception  of  the 
vis  viva  of  moving  masses,  we  are  prepared  for  the  an- 
nouncement that  the  heat  generated  by  the  collision  of  a 
falling  body  against  the  earth  is  proportional  to  the  vis 
viva  annihilated.  In  point  of  fact  it  is  not  an  annihilation 
at  all,  but  a  transference  of  vis  viva  from  the  mass,  to  its 
ultimate  particles.  This,  as  we  now  learn,  is  proportional 
to  the  square  of  the  velocity.  In  the  case,  therefore,  of  two 
cannon-balls  of  equal  weight,  if  one  strike  a  target  with 
twice  the  velocity  of  the  other,  it  will  generate  four  times 
the  heat ;  if  with  three  times  the  velocity,  it  will  generate 
nine  times  the  heat,  and  so  on. 

Mr.  Joule  has  shown  that  in  falling  from  a  height  of  772 
feet,  a  body  will  generate  an  amount  of  heat  sufficient  to 


THE  CONSTITUTION  OF  NATURE.  21 

raise  its  own  weight  of  water  one  degree  Fahrenheit  in 
temperature.  We  have  here  the  mechanical  equivalent  of 
heat.  Now,  a  body  falling  from  a  height  of  772  feet,  has, 
upon  striking  the  earth,  a  velocity  of  223  feet  a  second ; 
and  if  this  velocity  were  imparted  to  a  body,  by  any  other 
means,  the  quantity  of  heat  generated  by  the  stoppage  of 
its  motion  would  be  that  stated  above.  Six  times  that  ve- 
locity, or  1,338  feet,  would  not  be  an  inordinate  one  for  a 
cannon-ball  as  it  quits  the  gun ;  but  if  animated  by  six 
times  the  velocity,  thirty-six  times  the  heat  will  be  gener- 
ated by  the  stoppage  of  its  motion.  Hence  a  cannon-ball 
moving  with  a  velocity  of  1,338  feet  a  second,  would,  by 
collision,  generate  an  amount  of  heat  competent  to  raise  its 
own  weight  of  water  36  degrees  Fahrenheit  in  tempera- 
ture. If  composed  of  iron,  and  if  all  the  heat  generated 
were  concentrated  in  the  ball  itself,  its  temperature  would 
be  raised  about  360  degrees  Fahrenheit ;  because  one  de- 
gree in  the  case  of  water  is  equivalent  to  about  ten  de- 
grees in  the  case  of  iron.  In  artillery  practice  the  heat 
generated  is  usually  concentrated  upon  the  front  of  the 
bolt,  and  on  the  portion  of  the  target  first  struck.  By  this 
concentration  the  heat  developed  may  become  sufficiently 
intense  to  raise  the  dust  of  the  metal  to  incandescence,  a 
flash  of  light  often  accompanying  collision  with  the  target. 

Let  us  now  fix  our  attention  for  a  moment  on  the  gun- 
powder which  urges  the  cannon-ball.  This  is  composed  of 
combustible  matter,  which  if  burnt  in  the  open  air  would 
yield  a  certain  amount  of  heat.  It  will  not  yield  this 
amount  if  it  performs  the  work  of  urging  a  ball.  The  heat 
then  generated  by  the  gunpowder  will  fall  short  of  that 
produced  in  the  open  air,  by  an  amount  equivalent  to  the 
vis  viva  of  the  ball ;  and  this  exact  amount  is  restored  by 
the  ball  on  its  collision  with  the  target.  In  this  perfect 
way  are  heat  and  mechanical  motion  connected. 

Broadly  enunciated,  the  principle  of  the  conservation 


22  FRAGMENTS  OF  SCIENCE. 

of  force  asserts  that  the  quantity  of  force  in  the  universe  is 
as  unalterable  as  the  quantity  of  matter ;  that  it  is  alike 
impossible  to  create  force  and  to  annihilate  it.  But  in 
what  sense  are  we  to  understand  this  assertion  ?  It  would 
be  manifestly  inapplicable  to  the  force  of  gravity  as  New- 
ton defined  it ;  for  this  is  a  force  varying  inversely  as  the 
square  of  the  distance,  and  to  affirm  the  constancy  of  a 
varying  force  would  be  self-contradictory.  Yet,  when  the 
question  is  properly  understood,  gravity  forms  no  exception 
to  the  law  of  conservation.  Following  the  method  pur- 
sued by  Helmholtz,  I  will  here  attempt  an  elementary  ex- 
position of  this  law,  which,  though  destined  in  its  applica- 
tions to  produce  momentous  changes  in  human  thought,  is 
not  difficult  of  comprehension. 

For  the  sake  of  simplicity  we  will  consider  a  particle  of 
matter,  which  we  may  call  F,  to  be  perfectly  fixed,  and  a 
second  movable  particle,  D,  placed  at  a  distance  from  F. 
We  will  assume  that  these  two  particles  attract  each  other 
according  to  the  Newtonian  law.  At  a  certain  distance  the 
attraction  is  of  a  certain  definite  amount,  which  might  be 
determined  by  means  of  a  spring-balance.  At  half  this  dis- 
tance the  attraction  wrould  be  augmented  four  times  ;  at  a 
third  of  the  distance  it  would  be  augmented  nine  times  ;  at 
one-fourth  of  the  distance  sixteen  times,  and  so  on.  In 
every  case  the  attraction  might  be  measured  by  determin- 
ing, with  the  spring-balance,  the  amount  of  tension  which 
is  just  sufficient  to  prevent  D  from  moving  toward  F. 
Thus  far  we  have  nothing  whatever  to  do  with  motion ;  we 
deal  with  statics,  not  with  dynamics.  We  simply  take  into 
account  the  distance  of  D  from  Jf9  and  the  pull  exerted  by 
gravity  at  that  distance. 

It  is  customary  in  mechanics  to  represent  the  magni- 
tude of  a  force  by  a  line  of  a  certain  length,  a  force  of 
double  magnitude  being  represented  by  a  line  of  double 
length,  and  so  on.  Placing  then  the  particle  D  at  a  dis- 


THE   CONSTITUTION  OF  NATURE.  23 

tance  from  F,  we  can  in  imagination  draw  a  straight  line 
from  D  to  F,  and  at  D  erect  a  perpendicular  to  this  line, 
which  shall  represent  the  amount  of  the  attraction  exerted 
on  D  in  this  position.  If  D  be  at  a  very  great  distance 
from  F  the  attraction  will  be  very  small,  and  the  perpendic- 
ular consequently  very  short.  Let  us  now  suppose  that  at 
every  point  in  the  line  joining  F  and  D  a  perpendicular  is 
erected  proportional  in  length  to  the  attraction  exerted  at 
that  point ;  we  should  thus  obtain  an  infinite  number  of 
perpendiculars  of  gradually  increasing  length  as  D  ap- 
proaches F.  Uniting  the  ends  of  all  these  perpendiculars, 
we  should  obtain  a  curve,  and  between  this  curve  and  the 
straight  line  joining  F  and  D  we  should  have  an  area  con- 
taining all  the  perpendiculars  placed  side  by  side.  Each 
one  of  this  infinite  series  of  perpendiculars  representing  an 
attraction,  or  tension  as  it  is  sometimes  called,  the  area  just 
referred  to  represents  the  total  effort  capable  of  being  ex- 
erted by  the  tensions  upon  the  particle  D,  during  its  pas- 
sage from  its  first  position  up  to  F. 

Up  to  the  present  point  we  have  been  dealing  with  ten- 
sions, and  not  with  motion.  Thus  far  vis  viva  has  been 
entirely  foreign  to  our  contemplation  of  D  and  F.  Let  us 
now  suppose  D  placed  at  a  practically  infinite  distance  from 
F ;  here  the  pull  of  gravity  would  be  nothing,  and  the  per- 
pendicular representing  it  would  dwindle  to  a  point.  In 
this  position  the  sum  of  the  tensions  capable  of  being  ex- 
erted on  D  would  be  a  maximum.  Let  D  now  begin  to 
move  in  obedience  to  the  attraction  exerted  upon  it.  Mo- 
tion being  once  set  up,  the  idea  of  vis  viva  arises.  In 
moving  toward  F  the  particle  D  consumes,  as  it  were,  the 
tensions.  Let  us  fix  our  attention  on  D  at  any  point  of  the 
path  over  which  it  is  moving.  Between  that  point  and  F 
there  is  a  quantity  of  unused  tensions ;  beyond  that  point 
the  tensions  have  been  all  consumed,  but  we  have  in  their 
place  an  equivalent  quantity  of  vis  viva.  After  D  has 


24  FRAGMENTS  OF  SCIENCE. 

passed  any  point,  the  tension  previously  in  store  at  that 
point  disappears,  but  not  without  having  added,  during  the 
infinitely  small  duration  of  its  action,  a  due  amount  of 
motion  to  that  previously  possessed  by  D.  The  nearer  D 
approaches  to  F,  the  smaller  is  the  sum  of  the  tensions  re- 
maining, but  the  greater  is  the  living  force  ;  the  farther  D 
is  from  F,  the  greater  is  the  sum  of  the  unconsumed  ten- 
sions, and  the  less  is  the  living  force.  Now  the  principle 
of  conservation  affirms  not  the  constancy  of  the  value  of  the 
tensions  of  gravity,  nor  yet  the  constancy  of  the  vis  viva, 
taken  separately,  but  the  absolute  constancy  of  the  value 
of  the  sum  of  both.  At  the  beginning  the  vis  viva  was 
zero  and  the  tension  area  was  a  maximum ;  close  to  F  the 
vis  viva  is  a  maximum,  while  the  tension  area  is  zero.  At 
every  other  point  the  work-producing  power  of  the  particle 
D  consists  in  part  of  vis  viva  and  in  part  of  tensions. 

If  gravity,  instead  of  being  attraction,  were  repulsion, 
when  the  particles  are  in  contact,  the  sum  of  the  tensions 
between  two  material  particles  D  and  F  would  be  a  maxi- 
mum, and  the  vis  viva  zero.  If  D,  in  obedience  to  the 
repulsion,  moved  away  from  F,  vis  viva  would  be  gener- 
ated ;  and  the  farther  D  retreated  from  F  the  greater 
would  be  its  vis  viva,  and  the  less  the  amount  of  tension 
still  available  for  producing  motion.  Taking  repulsion  into 
account  as  well  as  attraction,  the  principle  of  the  conserva- 
tion of  force  affirms  that  the  mechanical  value  of  the  ten- 
sions and  vires  vivce  of  the  material  universe  is  a  constant 
quantity.  The  universe,  in  short,  possesses  two  kinds  of 
property  which  are  mutually  convertible,  at  an  unvarying 
rate.  The  diminution  of  either  carries  with  it  the  enhance- 
ment of  the  other,  the  total  value  of  the  property  remain- 
ing unchanged. 

The  considerations  that  we  have  here  applied  to  gravity 
apply  equally  to  chemical  affinity.  In  a  mixture  of  oxygen 
and  hydrogen  the  atoms  exist  apart,  but  by  the  application 


THE   CONSTITUTION  OF  NATURE.  25 

of  proper  means  they  may  be  caused  to  rush  together 
across  the  space  that  separates  them.  While  this  space 
exists,  and  as  long  as  the  atoms  have  not  begun  to  move 
toward  each  other,  we  have  tensions  and  nothing  else. 
During  their  motion  toward  each  other  the  tensions,  as  in 
the  case  of  gravity,  are  converted  into  vis  viva.  After 
they  clash  we  have  still  vis  viva,  but  in  another  form.  It 
was  translation,  it  is  vibration.  It  was  molecular  transfer, 
it  is  heat.  The  same  considerations  apply  to  a  mixture  of 
hydrogen  and  chlorine.  When  these  gases  are  mingled  in 
the  dark  they  remain  separate,  but  if  a  sunbeam  fall  upon 
the  mixture  the  atoms  rush  together  with  detonation. 
Here  also  we  have  tension  converted  into  molecular  trans- 
lation, and  molecular  translation  into  heat  and  sound. 

It  is  possible  to  reverse  these  processes,  to  unlock  the 
embrace  of  the  atoms  and  replace  them  in  their  first  posi- 
tions. But  to  accomplish  this  as  much  heat  would  be  re- 
quired as  was  generated  by  their  union.  Such  reversals 
occur  daily  and  hourly  in  Nature.  By  the  solar  waves,  the 
oxygen  of  water  is  divorced  from  its  hydrogen  in  the  leaves 
of  plants.  As  molecular  vis  viva  the  waves  disappear,  but 
in  so  doing  they  reendow  the  atoms  of  oxygen  and  hydro- 
gen with  tension.  The  atoms  are  thus  enabled  to  recom- 
bine,  and  when  they  do  so  they  restore  the  precise  amount 
of  heat  consumed  in  their  separation.  The  same  remarks 
apply  to  the  compound  of  carbon  and  oxygen,  called  car- 
bonic acid,  which  is  exhaled  from  our  lungs,  produced  by 
our  fires,  and  found  sparingly  diffused  everywhere  through- 
out the  air.  In  the  leaves  of  plants  the  sunbeams  also 
wrench  these  atoms  asunder,  and  sacrifice  themselves  in  the 
act ;  but  when  the  plants  are  burnt  the  amount  of  heat 
consumed  in  their  production  is  restored. 

This,  then,  is  the  rhythmic  play  of  Nature  as  regards 
her  forces.  Throughout  all  her  regions  she  oscillates  from 
tension  to  vis  viva,  from  vis  viva  to  tension.  We  have 
2 


26  FRAGMENTS  OF  SCIENCE. 

the  same  play  in  the  planetary  system.  The  earth's  orbit 
is  an  ellipse,  one  of  the  foci  of  which  is  occupied  by  the 
sun.  Imagine  the  earth  at  the  most  distant  part  of  the 
orbit.  Her  motion,  and  consequently  her  vis  viva,  is  then 
a  minimum.  The  planet  rounds  the  curve,  and  begins  to 
approach  the  sun.  In  front  it  has  a  store  of  tensions, 
which  is  gradually  consumed,  an  equivalent  amount  of  vis 
viva  being  generated.  When  nearest  to  the  sun  the  mo- 
tion, and  consequently  the  vis  viva,  is  a  maximum.  But 
here  the  available  tensions  have  been  used  up.  The  earth 
rounds  this  portion  of  the  curve  and  retreats  from  the  sun. 
Tensions  are  now  stored  up,  but  vis  viva  is  lost,  to  be  again 
restored  at  the  expense  of  the  complementary  force  on  the 
opposite  side  of  the  curve.  Thus  beats  the  heart  of  the 
universe,  but  without  increase  or  diminution  of  its  total 
stock  of  force. 

I  have  thus  far  tried  to  steer  clear  amid  confusion  by 
fixing  the  mind  of  the  reader  upon  things  rather  than  upon 
names.  But  good  names  are  essential ;  and  here,  as  yet, 
we  are  not  provided  with  such.  We  have  had  the  force  of 
gravity  and  living  force — two  utterly  distinct  things.  We 
have  had  pulls  and  tensions ;  and  we  might  have  had  the 
force  of  heat,  the  force  of  light,  the  force  of  magnetism,  or 
the  force  of  electricity — all  of  which  terms  have  been  em- 
ployed more  or  less  loosely  by  writers  on .  physics.  This 
confusion  is  happily  avoided  by  the  introduction  of  the 
term  "  energy,"  embracing  under  it  both  tension  and  vis 
viva.  Energy  is  possessed  by  bodies  already  in  motion ; 
it  is  then  actual,  and  we  agree  to  call  it  actual  or  dynamic 
energy.  It  is  our  old  vis  viva.  On  the  other  hand,  energy 
is  possible  to  bodies  not  in  motion,  but  which,  in  virtue  of 
attraction  or  repulsion,  possess  a  power  of  motion  which 
would  realize  itself  if  all  hinderances  were  removed. 
Looking,  for  example,  at  gravity,  a  body  on  the  earth's 
surface  in  a  position  from  which  it  cannot  fall  to  a  lower 


THE   CONSTITUTION   OF  NATURE.  27 

one  possesses  no  energy.  It  has  neither  motion  nor  power 
of  motion.  But  the  same  body  suspended  at  a  height 
above  the  earth  has  a  power  of  motion  though  it  may  not 
have  exercised  it.  Energy  is  possible  to  such  a  body,  and 
we  agree  to  call  this  potential  energy.  It  embraces  our  old 
tensions.  We,  moreover,  speak  of  the  conservation  of  en- 
ergy instead  of  the  conservation  of  force ;  and  say  that  the 
sum  of  the  potential  and  dynamic  energies  of  the  material 
universe  is  a  constant  quantity. 

A  body  cast  upward  consumes  the  actual  energy  of 
projection,  and  lays  up  potential  energy.  When  it  reaches 
its  utmost  height  all  its  actual  energy  is  consumed,  its 
potential  energy  being  then  a  maximum.  When  it  re- 
turns, there  is  a  reconversion  of  the  potential  into  the 
actual.  A  pendulum  at  the  limit  of  its  swing  possesses 
potential  energy ;  at  the  lowest  point  of  its  arc  its  energy 
is  all  actual.  A  patch  of  snow  resting  on  a  mountain-slope 
has  potential  energy ;  loosened,  and  shooting  down  as  an 
avalanche,  it  possesses  dynamic  energy.  The  pine-trees 
growing  on  the  Alps  have  potential  energy ;  but  rushing 
down  the  Holzrinne  of  the  wood-cutters  they  possess  actual 
energy.  The  same  is  true  of  the  mountains  themselves. 
As  long  as  the  rocks  wThich  compose  them  can  fall  to  a 
lower  level,  they  possess  potential  energy,  which  is  con- 
verted into  actual  when  the  frost  ruptures  their  cohesion 
and  hands  them  over  to  the  action  of  gravity.  The  hammer 
of  the  great  bell  of  Westminster,  when  raised  before  strik- 
ing, possesses  potential  energy  ;  when  it  falls,  the  energy 
becomes  dynamic ;  and  after  the  stroke,  we  have  the 
rhythmic  play  of  potential  and  dynamic  in  the  vibrations 
of  the  bell.  The  same  holds  good  for  the  molecular  oscilla- 
tions of  a  heated  body.  An  atom  is  pressed  against  its 
neighbor,  and  recoils.  But  the  ultimate  amplitude  of  the 
recoil  is  soon  attained,  the  motion  of  the  atom  in  that 
direction  is  checked,  and  for  an  instant  its  energy  is  all 


28  FRAGMENTS  OF  SCIENCE. 

potential.  It  is  then  drawn  toward  'its  neighbor  with 
accelerated  speed,  thus,  by  attraction,  converting  its  poten- 
tial into  dynamic  energy.  Its  motion  in  this  direction  is 
also  finally  checked,  and,  for  an  instant,  again  its  energy  is 
all  potential.  It  again  retreats,  converting,  by  repulsion, 
its  potential  into  dynamic  energy,  till  the  latter  attains  a 
maximum,  after  which  it  is  again  changed  into  potential 
energy.  Thus,  what  is  true  of  the  earth,  as  she  swings  to 
and  fro  in  her  yearly  journey  round  the  sun,  is  also  true  of 
her  minutest  atom.  We  have  wheels  within  wheels,  and 
rhythm  within  rhythm. 

When  a  body  is  heated,  a  change  of  molecular  arrange- 
ment always  occurs,  and  to  produce  this  change  heat  is 
consumed.  Hence,  a  portion  only  of  the  heat  communi- 
cated to  the  body  remains  as  dynamic  energy.  Looking 
back  on  some  of  the  statements  made  at  the  beginning  of 
this  article,  now  that  our  knowledge  is  more  extensive,  we 
see  the  necessity  of  qualifying  them.  When,  for  example, 
two  bodies  clash,  heat  is  generated ;  but  the  heat,  or  molec- 
ular dynamic  energy,  developed  at  the  moment  of  collision, 
is  not  the  equivalent  of  the  sensible  dynamic  energy  de- 
stroyed. The  true  equivalent  is  this  heat,  plus  the  potential 
energy  conferred  upon  the  molecules  by  the  placing  of 
greater  distances  between  them.  This  molecular  potential 
energy  is  afterward,  on  the  cooling  of  the  body,  converted 
into  heat. 

Wherever  two  atoms  capable  of  uniting  together  by 
their  mutual  attractions  exist  separately,  they  form  a  store 
of  potential  energy.  Thus  our  woods,  forests,  and  coal- 
fields on  the  one  hand,  and  our  atmospheric  oxygen  on  the 
other,  constitute  a  vast  store  of  energy  of  this  kind — vast, 
but  far  from  infinite.  We  have,  besides  our  coal-fields, 
bodies  in  the  metallic  condition  more  or  less  sparsely  dis- 
tributed in  the  earth's  crust.  These  bodies  can  be  oxidized, 
and  hence  are,  so  far  as  they  go,  stores  of  potential  energy. 


THE  CONSTITUTION  OF  NATURE.  29 

But  the  attractions  of  the  great  mass  of  the  earth's  crust 
are  already  satisfied,  and  from  them  no  further  energy  can 
possibly  be  obtained.  Ages  ago  the  elementary  constitu- 
ents of  our  rocks  clashed  together  and  produced  the  motion 
of  heat,  which  was  taken  up  by  the  ether  and  carried  away 
through  stellar  space.  It  is  lost  forever  as  far  as  we  are 
concerned.  In  those  ages  the  hot  conflict  of  carbon, 
oxygen,  and  calcium,  produced  the  chalk  and  limestone 
hills  which  are  now  cold ;  and  from  this  carbon,  oxygen, 
and  calcium,  no  further  energy  can  be  derived.  And  so  it 
is  with  almost  all  the  other  constituents  of  the  earth's 
crust.  They  took  their  present  form  in  obedience  to  mo- 
lecular force ;  they  turned  their  potential  energy  into  dy- 
namic, and  gave  it  to  the  universe  ages  before  man 
appeared  upon  this  planet.  For  him  a  residue  of  potential 
energy  remains,  vast  truly  in  relation  to  the  life  and  wants 
of  an  individual,  but  exceedingly  minute  in  comparison 
with  the  earth's  primitive  store. 

To  sum  up.  The  whole  stock  of  energy  or  worJeing- 
power  in  the  world  consists  of  attractions,  repulsions,  and 
motions.  If  the  attractions  and  repulsions  are  so  circum- 
stanced as  to  be  able  to  produce  motion,  they  are  sources 
of  working-power,  but  not  otherwise.  As  stated  a  moment 
ago,  the  attraction  exerted  between  the  earth  and  a  body 
at  a  distance  from  the  earth's  surface  is  a  source  of  working- 
power;  because  the  body  can  be  moved  by  the  attraction, 
and  in  falling  to  the  earth  can  perform  work.  When  it 
rests  upon  the  earth's  surface  it  is  not  a  source  of  power  or 
energy,  because  it  can  fall  no  farther.  But  though  it  has 
ceased  to  be  a  source  of  energy,  the  attraction  of  gravity  still 
acts  as  &  force,  which  holds  the  earth  and  weight  together. 

The  same  remarks  apply  to  attracting  atoms  and  mole- 
cules. As  long  as  distance  separates  them,  they  can  move 
across  it  in  obedience  to  the  attraction,  and  the  motion 
thus  produced  may,  by  proper  appliances,  be  caused  to 


30  FRAGMENTS  OF  SCIENCE. 

perform  mechanical  work.  When,  for  example,  two  atoms 
of  hydrogen  unite  with  one  of  oxygen,  to  form  water,  the 
atoms  are  first  drawn  toward  each  other — they  move,  they 
clash,  and  then,  by  virtue  of  their  resiliency,  they  recoil  and 
quiver.  To  this  quivering  motion  we  give  the  name  of 
heat.  Now  this  atomic  vibration  is  merely  the  redistribu- 
tion of  the  motion  produced  by  the  chemical  affinity ;  and 
this  is  the  only  sense  in  which  chemical  affinity  can  be  said 
to  be  converted  into  heat.  We  must  not  imagine  the 
chemical  attraction  destroyed,  or  converted  into  any  thing 
else.  For  the  atoms  when  mutually  clasped  to  form  a 
molecule  of  water,  are  held  together  by  the  very  attraction 
which  first  drew  them  toward  each  other.  That  which  has 
really  been  expended  is  the  pull  exerted  through  the  space  by 
which  the  distance  between  the  atoms  has  been  diminished. 

If  this  be  understood  it  will  be  at  once  seen  that  gravity 
may  in  this  sense  be  said  to  be  convertible  into  heat ;  that 
it  is  in  reality  no  more  an  outstanding  and  inconvertible 
agent,  as  it  is  sometimes  stated  to  be,  than  chemical  affin- 
ity. By  the  exertion  of  a  certain  pull  through  a  certain 
space  a  body  is  caused  to  clash  with  a  certain  definite 
velocity  against  the  earth.  Heat  is  thereby  developed, 
and  this  is  the  only  sense  in  which  gravity  can  be  said  to 
be  converted  into  heat.  In  no  case  is  the  force  which  pro- 
duces the  motion  annihilated  or  changed  into  any  thing 
else.  The  mutual  attraction  of  the  earth  and  weight  exists 
when  they  are  in  contact  as  when  they  were  separate ; 
but  the  ability  of  that  attraction  to  employ  itself  in  the 
production  of  motion  does  not  exist. 

The  transformation,  in  this  case,  is  easily  followed  by 
the  mind's  eye.  First,  the  weight  as  a  whole  is  set  in 
motion  by  the  attraction  of  gravity.  This  motion  of  the 
mass  is  arrested  by  collision  with  the  earth,  being  broken  up 
into  molecular  tremors,  to  which  we  give  the  name  of  heat. 

And  when  we  reverse  the  process,  and  employ  those 


THE   CONSTITUTION  OF  NATURE.  31 

tremors  of  heat  to  raise  a  weight,  as  is  done  through  the 
intermediation  of  an  elastic  fluid  in  the  steam-engine,  a 
certain  definite  portion  of  the  molecular  motion  is  de- 
stroyed in  raising  the  weight.  In  this  sense,  and  this  sense 
only,  can  the  heat  be  said  to  be  converted  into  gravity,  or, 
more  correctly,  into  potential  energy  of  gravity.  It  is  not 
that  the  destruction  of  the  heat  has  created  any  new 
attraction,  but  simply  that  the  old  attraction  has  now  a 
power  conferred  upon  it,  of  exerting  a  certain  definite  pull 
in  the  interval  between  the  starting-point  of  the  falling 
weight  and  its  collision  with  the  earth. 

When,  therefore,  writers  on  the  conservation  of  energy 
speak  of  tensions  being  "  consumed "  and  "  generated," 
they  do  not  mean  thereby  that  old  attractions  have  been  an- 
nihilated, and  new  ones  brought  into  existence,  but  that, 
in  the  one  case,  the  power  of  the  attraction  to  produce 
motion  has  been  diminished  by  the  shortening  of  the  dis- 
tance between  the  attracting  bodies,  and  that  in  the  other 
case  the  power  of  producing  motion  has  been  augmented 
by  the  increase  of  the  distance.  These  remarks  apply  to 
all  bodies,  whether  they  be  sensible  masses  or  molecules. 

Of  the  inner  quality  that  enables  matter  to  attract 
matter  we  know  nothing;  and  the  law  of  conservation 
makes  no  statement  regarding  that  quality.  It  takes  the 
facts  of  attraction  as  they  stand,  and  affirms  only  the  con- 
stancy of  working-power.  That  power  may  exist  in  the 
form  of  MOTION  ;  or  it  may  exist  in  the  form  of  FORCE,  with 
distance  to  act  through.  The  former  is  dynamic  energy, 
the  latter  is  potential  energy,  the  constancy  of  the  sum  of 
both  being  affirmed  by  the  law  of  conservation.  The  con- 
vertibility of  natural  forces  consists  solely  in  transforma- 
tions of  dynamic  into  potential,  and  of  potential  into  dy- 
namic energy,  which  are  incessantly  going  on.  In  no  other 
sense  has  the  convertibility  of  force,  at  present,  any  scien- 
tific meaning. 


II. 

THOUGHTS  ON  PRAYER  AND  NATURAL 
LAW. 

AN  EXTRACT. 
[Mountaineering  in  1861,  p.  33.] 


'Aber  im  stillen  Gemach  entwirft  bedcutendc  Zirkel 

Sinnend  der  Weise. 

Folgt  durcli  die  Liifte  dem  Klang,  folgt  durch  den  Aether  dem  Stralil, 

Sucht  das  vertraute  Gesetz  in  des  Zufalls  grausenden  Wundern, 

Sucht  den  ruhenden  Pol  in  der  Erscheinungen  Flucht." 

SCHILLER. 


II. 

PRAYER  AND  NATURAL  LAW. 

THE  aspects  of  Nature  are  more  varied  and  impressive 
in  Alpine  regions  than  elsewhere.  The  mountains  in  their 
setting  of  deep-blue  sky ;  the  glow  of  firmament  and  peaks 
at  sunrise  and  sunset ;  the  formation  and  distribution  of 
clouds  ;  the  descent  of  rain,  hail,  and  snow ;  the  stealthy 
slide  of  glaciers  and  the  rush  of  avalanches  and  rivers ; 
the  fury  of  storms ;  thunder  and  lightning,  with  their 
occasional  accompaniment  of  blazing  woods  —  all  these 
things  tend  to  excite  the  feelings  and  to  bewilder  the  mind. 
In  this  entanglement  of  phenomena  it  seems  hopeless  to 
seek  for  law  or  orderly  connection.  And  before  the 
thought  of  law  dawned  upon  the  human  mind  men  natu- 
rally referred  these  inexplicable  effects  to  personal  agency. 
The  savage  saw  in  the  fall  of  a  cataract  the  leap  of  a  spirit, 
and  the  echoed  thunder-peal  was  to  him  the  hammer-clang 
of  an  exasperated  god.  Propitiation  of  these  terrible 
powers  was  the  consequence,  and  sacrifice  was  offered  to 
the  demons  of  earth  and  air. 

But  observation  tends  to  chasten  the  emotions  and  to 
check  those  structural  efforts  of  the  intellect  which  have 
emotion  for  their  base.  One  by  one  natural  phenomena 
have  been  associated  with  their  proximate  causes;  and 
the  idea  of  direct  personal  volition  mixing  itself  in  the! 
economy  of  Nature  is  retreating  more  and  more.  Many  of 
us  fear  this  tendency ;  our  faith  and  feelings  are  dear  to  us, 


36  FRAGMENTS  OF  SCIENCE. 

and  we  look  with  suspicion  and  dislike  on  any  philosophy, 
the  apparent  tendency  of  which  is  to  dry  up  the  soul. 
Probably  every  change  from  ancient  savagery  to  our  present 
enlightenment  excited,  in  a  greater  or  less  degree,  a  fear 
of  this  kind.  But  the  fact  is,  that  we  have  not  yet  deter- 
mined whether  the  form  under  which  they  now  appear  in 
the  world  is  necessary  to  the  life  and  warmth  of  religious 
feeling.  We  may  err  in  linking  the  imperishable  with  the 
transitory,  and  confound  the  living  plant  with  the  decaying 
r  -pole  to  which  it  clings.  My  object,  however,  at  present  is 
j  not  to  argue,  but  to  mark  a  tendency.  We  have  ceased  to 
propitiate  the  powers  of  Nature — ceased  even  to  pray  for 
things  in  manifest  contradiction  to  natural  laws.  In  Prot- 
estant countries,  at  least,  I  think  it  is  conceded  that  the 
age  of  miracles  is  past. 

The  general  question  of  miracles  is  at  present  in  able 
and  accomplished  hands ;  and  were  it  not  so,  my  polemical 
acquirements  are  so  limited,  that  I  should  not  presume  to 
enter  upon  a  discussion  of  this  subject  on  its  entire  merits. 
But  there  is  one  little  outlying  point,'  which  attaches  itself 
x  to  this  question,  on  which  a  student  of  science,  without 
quitting  the  ground  which  strictly  belongs  to  him,  may 
offer  a  remark. 

At  the  auberge  near  the  foot  of  the  Rhone  glacier,  I 
met,  in  the  summer  of  1858,  an  athletic  young  priest,  who, 
after  a  solid  breakfast,  including  a  bottle  of  wine,  informed 
me  that  he  had  come  up  to  "  bless  the  mountains."  This 
was  the  annual  custom  of  the  place.  Year  by  year  the 
Highest  was  entreated,  by  official  intercessors,  to  make 
such  meteorological  arrangements  as  should  insure  food 
and  shelter  for  the  flocks  and  herds  of  the  Valaisians.  A 
diversion  of  the  Rhone,  or  a  deepening  of  the  river's  bed, 
would  have  been  of  incalculable  benefit  to  the  inhabitants 
of  the  valley  at  the  time  I  now  mention.  But  the  priest 
would  have  shrunk  from  the  idea  of  asking  the  Omnipo- 


PRAYER  AND   NATURAL  LAW.  37 

tent  to  open  a  new  channel  for  the  river,  or  to  cause  a 
portion  of  it  to  flow  over  the  Grimsel  Pass,  and  down  the 
vale  of  Oberhasli  to  Brientz.  This  he  would  have  deemed 
a  miracle,  and  he  did  not  come  to  ask  the  Creator  to  per- 
form miracles,  but  to  do  something  which  he  manifestly 
thought  lay  quite  within  the  bounds  of  the  natural  and 
non-miraculous.  A  Protestant  gentleman,  who  was  present 
at  the  time,  smiled  at  this  recital.  He  had  no  faith  in  the 
priest's  blessing,  still  he  deemed  his  prayer  different  in 
kind  from  a  request  to  open  a  new  river-cut,  or  to  cause 
the  water  to  flow  up-hill. 

In  a  similar  manner  we  Protestants  smile  at  the  honest 
Tyrolese  priest,  who,  when  he  feared  the  bursting  of  a 
glacier-dam,  offered  the  sacrifice  of  the  mass  upon  the  ice 
as  a  means  of  averting  the  calamity.  That  poor  man  did 
not  expect  to  convert  the  ice  into  adamant,  or  to  strengthen 
its  texture  so  as  to  enable  it  to  withstand  the  pressure  of 
the  water ;  nor  did  he  expect  that  his  sacrifice  would  cause 
the  stream  to  roll  back  upon  its  source  and  relieve  him,  by 
a  miracle,  of  its  presence.  But  beyond  the  boundaries  of 
his  knowledge  lay  a  region  where  rain  wTas  generated,  he 
knew  not  how.  He  was  not  so  presumptuous  as  to  expect 
a  miracle,  but  he  firmly  believed  that  in  yonder  cloud-land 
matters  could  be  so  arranged,  without  trespass  on  the 
miraculous,  that  the  stream  which  threatened  him  and  his 
flock  should  be  caused  to  shrink  within  its  proper  bounds. 

Both  these  priests  fashioned  that  which  they  did  not 
understand  to  their  respective  wants  and  wishes.  In  their 
case  imagination  wrought,  unconditioned  by  a  knowledge 
of  laws.  A  similar  state  of  mind  was  long  prevalent 
among  mechanicians ;  many  of  whom,  and  some  of  them 
extremely  skilful  ones,  were  occupied  a  century  ago  with 
the  question  of  a  perpetual  motion.  They  aimed  at  con- 
structing a  machine  which  should  execute  work  without 
the  expenditure  of  power ;  and  many  of  them  went  mad 


38  FRAGMENTS  OF  SCIENCE. 

in  the  pursuit  of  this  object.  The  faith  in  such  a  consum- 
mation, involving  as  it  did  immense  personal  interest  to 
the  inventor,  was  extremely  exciting,  and  every  attempt  to 
destroy  this  faith  was  met  by  bitter  resentment  on  the 
part  of  those  who  held  it.  Gradually,  however,  as  men 
became  more  and  more  acquainted  with  the  true  functions 
of  machinery,  the  dream  dissolved.  The  hope  of  getting 
work  out  of  mere  mechanical  combinations  disappeared; 
but  still  there  remained  for  the  speculator  a  cloud-land 
denser  than  that  which  filled  the  imagination  of  the  Tyrol- 
ese  priest,  and  out  of  which  he  still  hoped  to  evolve  per- 
petual motion.  There  was  the  mystic  store  of  chemic 
force,  which  nobody  understood;  there  were  heat  and 
light,  electricity  and  magnetism,  all  competent  to  produce 
mechanical  motions.1  Here,  then,  is  the  mine  in  which 
we  must  seek  our  gem.  A  modified  and  more  refined  form 
of  the  ancient  faith  revived ;  and,  for  aught  I  know,  a  rem- 
nant of  sanguine  designers  may  at  the  present  moment  be 
engaged  on  the  problem  which  like-minded  men  in  former 
years  left  unsolved. 

And  why  should  a  perpetual  motion,  even  under  modern 
conditions,  be  impossible  ?  The  answer  to  this  question  is 
the  statement  of  that  great  generalization  of  modern  sci- 
ence, which  is  known  under  the  name  of  the  Conservation 
of  Energy.  This  principle  asserts  that  no  power  can  make 
its  appearance  in  Nature  without  an  equivalent  expenditure 
of  some  other  power ;  that  natural  agents  are  so  related  to 
each  other  as  to  be  mutually  convertible,  but  that  no  new 
agency  is  created.  Light  runs  into  heat ;  heat  into  elec- 
tricity ;  electricity  into  magnetism ;  magnetism  into  me- 
chanical force ;  and  mechanical  force  again  into  light  and 
heat.  The  Proteus  changes,  but  he  is  ever  the  same ;  and 
his  changes  in  Nature,  supposing  no  miracle  to  supervene, 
are  the  expression,  not  of  spontaneity,  but  of  physical  neces- 
1  See  Helmholtz— "  Wechselwirkung  der  Naturkrafte." 


PRAYER  AND   NATURAL  LAW.  39 

sity.  A  perpetual  motion,  then,  is  deemed  impossible,  be- 
cause it  demands  the  creation  of  force,  whereas  the  principle 
of  Conservation  is,  no  creation  but  infinite  conversion. 

It  is  an  old  remark  that  the  law  which  moulds  a  tear 
also  rounds  a  planet.  In  the  application  of  law  in  Nature 
the  terms  great  and  small  are  unknown.  Thus  the  principle 
referred  to  teaches  us  that  the  Italian  wind  gliding  over 
the  crest  of  the  Matterhorn  is  as  firmly  ruled  as  the  earth 
in  its  orbital  revolution  round  the  sun ;  and  that  the  fall  of 
its  vapor  into  clouds  is  exactly  as  much  a  matter  of  neces- 
sity as  the  return  of  the  seasons.  The  dispersion,  there- 
fore, of  the  slightest  mist  by  the  special  volition  of  the 
Eternal,  would  be  as  much  a  miracle  as  the  rolling  of  the 
Rhone  over  the  Grimsel  precipices  and  down  Haslithal  to 
Brientz. 

It  seems  to  me  quite  beyond  the  present  power  of 
science,  to  demonstrate  that  the  Tyrolese  priest,  or  his 
colleague  of  the  Rhone  valley,  asked  for  an  "  impossibility  " 
in  praying  for  good  weather ;  but  science  can  demonstrate 
the  incompleteness  of  the  knowledge  of  Nature  wrhich 
limited  their  prayers  to  this  narrow  ground  ;  and  she  may 
lessen  the  number  of  instances  in  which  we  "  ask  amiss," 
by  showing  that  we  sometimes  pray  for  the  performance 
of  a  miracle  when  we  do  not  intend  it.  She  does  assert, 
for  example,  that,  without  a  disturbance  of  natural  law, 
quite  as  serious  as  the  stoppage  of  an  eclipse,  or  the  rolling 
of  the  St.  Lawrence  up  the  Falls  of  Niagara,  no  act  of 
humiliation,  individual  or  national,  could  call  one  shower 
from  heaven,  or  deflect  toward  us  a  single  beam  of  the  sun. 

Those,  therefore,  who  believe  that  the  miraculous  is  still 
active  in  Nature,  may,  with  perfect  consistency,  join  in  our 
periodic  prayers  for  fair  weather  and  for  rain :  while  those 
who  hold  that  the  age  of  miracles  is  past,  will  refuse  to 
join  in  such  petitions.  And  if  these  latter  wish  to  fall  back 
upon  such  a  justification,  they  may  fairly  urge  that  the 


40  FRAGMENTS  OF  SCIENCE. 

latest  conclusions  of  science  are  in  perfect  accordance  with 
the  doctrine  of  the  Master  Himself,  which  manifestly  was 
that  the  distribution  of  natural  phenomena  is  not  affected 
by  moral  or  religious  causes.  "  He  maketh  His  sun  to  rise 
on  the  evil  and  on  the  good,  and  sendeth  rain  on  the  just 
and  on  the  unjust."  Granting  "  the  power  of  Free-will  in 
man,"  so  strongly  claimed  by  Professor  Mansel  in  his  ad- 
mirable defence  of  the  belief  in  miracles,  and  assuming  the 
efficacy  of  free  prayer  to  produce  changes  in  external 
Nature,  it  necessarily  follows  that  natural  laws  are  more  or 
less  at  the  mercy  of  man's  volition,  and  no  conclusion 
founded  on  the  assumed  permanence  of  those  laws  would 
be  worthy  of  confidence. 

It  is  a  wholesome  sign  for  England  that  she  numbers 
among  her  clergy  men  wise  enough  to  understand  all  this, 
and  courageous  enough  to  act  up  to  their  knowledge. 
Such  men  do  service  to  the  public  character  by  encourag- 
ing a  manly  and  intelligent  conflict  with  the  causes  of 
disease  and  scarcity,  instead  of  a  delusive  reliance  on 
supernatural  aid.  But  they  have  also  a  value  beyond  this 
local  and  temporary  one.  They  prepare  the  public  mind 
for  changes  which,  though  inevitable,  could  hardly,  without 
such  preparation,  be  wrought  without  violence.  Iron  is 
strong ;  still,  water  in  crystallizing  will  shiver  an  iron 
envelope,  and  the  more  unyielding  the  metal  is,  the  worse 
for  its  safety.  There  are  men  among  us  who  would  encom- 
pass philosophic  speculation  by  a  rigid  envelope,  hoping- 
thereby  to  restrain  it,  but  in  reality  giving  it  explosive 
force.  If  we  want  an  illustration  of  this  we  have  only  to 
look  at  modern  Rome.  In  England,  thanks  to  men  of  the 
stamp  to  which  I  have  alluded,  scope  is  gradually  given  to 
thought  for  changes  of  aggregation,  and  the  envelope 
slowly  alters  its  form  in  accordance  with  the  necessities  o/ 
the  time. 


THE  proximate  origin  of  the  foregoing  slight  article,  and  probably  the 
remoter  origin  of  the  next  following  one,  was  this :  Some  years  ago,  a 
day  of  prayer  and  humiliation,  on  account  of  a  bad  harvest,  was  ap- 
pointed by  the  proper  religious  authorities ;  but  certain  clergymen  of  the 
Church  of  England,  doubting  the  wisdom  of  the  demonstration,  declined 
to  join  in  the  services  of  the  day.  For  this  act  of  nonconformity  they 
were  severely  censured  by  some  of  their  brethren.  Rightly  or  wrongly, 
my  sympathies  were  on  the  side  of  these  men ;  and,  to  lend  them  a  help- 
ing hand  in  their  struggle  against  odds,  I  inserted  the  foregoing  chapter 
in  the  little  book  mentioned  on  the  title-page.  Some  time  subsequently 
I  received  from  a  gentleman  of  great  weight  and  distinction  in  the  scien- 
tific world,  and,  I  believe,  of  perfect  orthodoxy  in  the  religious  one,  a 
note  directing  my  attention  to  an  exceedingly  thoughtful  article  on 
Prayer  and  Cholera  in  the  Pall  Mall  Gazette.  My  eminent  correspondent 
deemed  the  article  a  fair  answer  to  the  remarks  made  by  me  in  1861. 
I  also  was  struck  by  the  temper  and  ability  of  the  article,  but  I  could 
not  deem  its  arguments  satisfactory,  and,  in  a  short  note  to  the  editor  of 
the  Pall  Mall  Gazette,  I  ventured  to  state  so  much.  This  letter  elicited 
some  very  able  replies,  and  a  second  leading  article  was  also  devoted  to 
the  subject.  In  answer  to  all,  I  risked  the  publication  of  a  second  letter, 
and  soon  afterward,  by  an  extremely  courteous  note  from  the  editor,  the 
discussion  was  closed. 

Though  thus  stopped  locally,  the  discussion  flowed  in  other  directions. 
Sermons  were  preached,  essays  were  published,  articles  were  written, 
while  a  copious  correspondence  occupied  the  pages  of  some  of  the  re- 
ligious newspapers.  It  gave  me  sincere  pleasure  to  notice  that  the  dis- 
cussion, save  in  a  few  cases  where  natural  coarseness  had  the  upper 
hand,  was  conducted  with  a  minimum  of  vituperation.  The  severity 
shown  was  hardly  more  than  sufficient  to  demonstrate  earnestness,  while 
gentlemanly  feeling  was  too  predominant  to  permit  that  earnestness  to 
contract  itself  to  bigotry  or  to  clothe  itself  in  abuse.  It  was  probably 
the  memory  of  this  discussion  which  caused  another  excellent  friend  of 
mine  to  recommend  to  my  perusal  the  exceedingly  able  work  which  in 
the  next  article  I  have  endeavored  to  review. 


IIL 
MIRACLES  AND  SPECIAL  PROVIDENCES. 

A  REVIEW. 
[Fortnightly  Review,  New  Series,  vol.  i.,  p.  645.] 


"  Mr.  Mozley's  book  belongs  to  that  class  of  writing  of  which  Butler 
may  be  taken  as  the  type.  It  is  strong,  genuine  argument  about  difficult 
matters,  fairly  tracing  what  is  difficult,  fairly  trying  to  grapple,  not  with 
what  appears  the  gist  and  strong  point  of  a  question,  but  with  what  really 
at  bottom  is  the  knot  of  it.  It  is  a  book  the  reasoning  of  which  may  not 
satisfy  every  one.  .  .  .  But  we  think  it  is  a  book  for  people  who  wish  to 
see  a  great  subject  handled  on  a  scale  which  befits  it,  and  with  a  percep- 
tion of  its  real  elements.  It  is  a  book  which  will  have  attractions  for 
those  who  like  to  see  a  powerful  mind  applying  itself,  without  shrinking 
or  holding  back,  without  trick,  or  reserve,  or  show  of  any  kind,  as  a 
wrestler  closes  body  to  body  with  his  antagonist,  to  the  strength  of  an 
adverse  and  powerful  argument." — The  Times,  Tuesday,  June  5,  1866. 

"  We  should  add,  that  the  faults  of  the  work  are  wholly  on  the  surface 
and  in  the  arrangement ;  that  the  matter  is  as  solid  and  as  logical  as  that 
of  any  book  within  recent  memory,  and  that  it  abounds  in  striking  pas- 
sages, of  which  we  have  scarcely  been  able  even  to  give  a  sample.  No 
future  arguer  against  miracles  can  afford  to  pass  it  over." — Saturday  Re- 
view, September  15,  1866. 


III. 

MIRACLES  AND  SPECIAL  PROVIDENCES. 

IT  is  my  privilege  to  enjoy  the  friendship  of  a  select 
number  of  religious  men,  with  whom  I  converse  frankly 
upon  theological  subjects,  expressing  without  disguise  the 
notions  and  opinions  I  entertain  regarding  their  tenets,  and 
hearing  in  return  these  notions  and  opinions  subjected  to 
criticism.  I  have  thus  far  found  them  liberal  and  loving 
men,  patient  in  hearing,  tolerant  in  reply,  who  know  how 
to  reconcile  the  duties  of  courtesy  with  the  earnestness  of 
debate.  From  one  of  these,  nearly  a  year  ago,  I  received 
a  note,  recommending  strongly  to  my  attention  the  volume 
of  "  Bampton  Lectures  "  for  1865,  in  which  the  question  of 
miracles  is  treated  by  Mr.  Mozley.  Previous  to  receiving 
this  note,  I  had  in  part  made  the  acquaintance  of  the  work, 
through  the  able  and  elaborate  review  of  it  which  had  ap- 
peared in  the  Times.  The  combined  effect  of  the  letter 
and  the  review  was  to  make  the  book  the  companion  of 
my  summer  tour  in  the  Alps.  There,  during  the  wet  and 
snowy  days  which  were  only  too  prevalent  last  year,  and 
during  the  days  of  rest  interpolated  between  days  of  toil, 
I  made  myself  more  thoroughly  conversant  with  Mr.  Moz- 
ley's  volume.  I  found  it  clear  and  strong — an  intellectual 
tonic,  as  bracing  and  pleasant  to  my  mind  as  the  keen  air 
of  the  mountains  was  to  my  body.  From  time  to  time  I 
jotted  down  my  thoughts  regarding  it,  intending  afterward, 
if  time  permitted,  to  work  them  up  into  a  coherent  whole. 


46  FRAGMENTS  OF  SCIENCE. 

Other  duties,  however,  interfered  with  the  carrying  out  of 
this  intention,  and  what  I  wrote  last  summer  I  now  pub- 
lish, not  hoping  within  any  reasonable  time  to  be  able  to 
render  my  defence  of  scientific  method  more  complete. 

Mr.  Mozley  refers  at  the  outset  of  his  task  to  the  move- 
ment against  miracles  which  of  late  years  has  taken  place, 
and  which  determined  his  choice  of  a  subject.  He  acquits 
modern  science  of  having  had  any  great  share  in  the  pro- 
duction of  this  movement.  The  objection  against  miracles, 
he  says,  does  not  arise  from  any  minute  knowledge  of  the 
laws  of  Nature,  but  simply  because  they  are  opposed  to 
that  plain  and  obvious  order  of  Nature  which  everybody 
sees.  The  present  movement  is,  he  thinks,  to  be  ascribed  to 
the  greater  earnestness  and  penetration  of  the  present  age. 
Formerly  miracles  were  accepted  without  question,  because 
without  reflection ;  but  the  exercise  of  what  Mr.  Mozley 
calls  the  historic  imagination  is  a  characteristic  of  our  own 
time.  Men  are  now  accustomed  to  place  before  themselves 
vivid  images  of  historic  facts,  and  when  a  miracle  rises  to 
view,  they  halt  before  the  astounding  occurrence,  and  real- 
izing it  with  the  same  clearness  as  if  it  were  now  passing 
before  their  eyes,  they  ask  themselves,  "  Can  this  have 
taken  place  ?  "  In  some  instances  the  effort  to  answer  this 
question  has  led  to  a  disbelief  in  miracles,  in  others  to  a 
strengthening  of  belief.  The  end  and  aim  of  Mr.  Mozley's 
lectures  is  to  show  that  the  strengthening  of  belief  is  the 
logical  result  which  ought  to  follow  from  the  examination 
of  the  facts. 

Attempts  have  been  made  by  religious  men  to  bring 
the  Scripture  miracles  within  the  scope  of  the  order  of 
Nature,  but  all  such  attempts  are  rejected  by  Mr.  Mozley 
as  utterly  futile  and  wide  of  the  mark.  Regarding  mira- 
cles as  a  necessary  accompaniment  of  a  revelation,  their 
evidential  value  in  his  eyes  depends  entirely  upon  their 
deviation  from  the  order  of  Nature.  Thus  deviating,  they 


MIRACLES  AND   SPECIAL  PROVIDENCES.  47 

suggest  and  illustrate  to  him  a  power  higher  than  Nature, 
a  "  personal  will ; "  and  they  commend  the  person  in  whom 
this  power  is  vested  as  a  messenger  from  on  high.  With- 
out these  credentials  such  a  messenger  would  have  no  right 
to  demand  belief,  even  though  his  assertion  regarding  his 
divine  mission  were  backed  by  a  holy  life.  Nor  is  it  by 
miracles  alone  that  the  order  of  Nature  is,  or  may  be,  dis- 
turbed. The  material  universe  is  also  the  arena  of  "  spe- 
cial providences."  Under  these  two  heads  Mr.  Mozley  dis- 
turbs the  total  preternatural.  One  form  of  the  preternatural 
may  shade  into  the  other,  as  one  color  passes  into  another 
in  the  rainbow ;  but  while  the  line  which  divides  the  spe- 
cially providential  from  the  miraculous  cannot  be  sharply 
drawn,  their  distinction  broadly  expressed  is  this,  that 
while  a  special  providence  can  only  excite  surmise  more 
or  less  probable,  it  is  "  the  nature  of  a  miracle  to  give 
proof,  as  distinguished  from  mere  surmise  of  divine  de- 
sign." ^ 

Mr.  Mozley  adduces  various  illustrations  of  what  he  re- 
gards to  be  special  providences  as  distinguished  from  mira- 
cles. "  The  death  of  Arius,"  he  says,  "  was  not  miraculous, 
because  the  coincidence  of  the  death  of  a  heresiarch  taking- 
place  when  it  was  peculiarly  advantageous  to  the  orthodox 
faith  ....  was  not  such  as  to  compel  the  inference  of  ex- 
traordinary Divine  agency ;  but  it  was  a  special  providence, 
because  it  carried  a  reasonable  appearance  of  it.  The  mir- 
acle of  the  Thundering  Legion  was  a  special  providence, 
but  not  a  miracle,  for  the  same  reason,  because  the  coinci- 
dence of  an  instantaneous  fall  of  rain  in  answer  to  prayer 
carried  some  appearance,  but  not  proof,  of  preternatural 
agency."  The  eminent  lecturer's  remarks  on  this  head 
brought  to  my  recollection  certain  narratives  published  in 
Methodist  magazines,  which  I  used  to  read  with  avidity 
when  a  boy.  The  title  of  these  chapters,  if  I  remember 
right,  was  "  The  Providence  of  God  asserted,"  and  in  them 


48  FRAGMENTS  OF  SCIENCE. 

the  most  extraordinary  and  exciting  escapes  from  peril  were 
recounted  and  ascribed  to  prayer,  while  equally  wonderful 
instances  of  calamity  were  adduced  as  illustrations  of  Di- 
vine retribution.  In  such  magazines,  or  elsewhere,  I  found 
recorded  the  case  of  the  celebrated  Samuel  Hick,  which,  as 
it  illustrates  a  whole  class  of  special  providences,  approach- 
ing in  conclusiveness  to  miracles,  is  worthy  of  mention  here. 
It  is  related  of  this  holy  man — and  I,  for  one,  have  no  doubt 
of  his  holiness — that  flour  was  lacking  to  make  the  sacra- 
mental bread.-  Grain  was  present,  and  a  windmill  was 
present,  but  there  was  no  wind  to  grind  the  corn.  With 
faith,  undoubting  Samuel  Hick  prayed  to  the  Lord  of  the 
winds :  the  sails  turned,  the  corn  was  ground,  after  which 
the  wind  ceased.  According  to  the  canon  of  the  Bampton 
Lecturer,  this,  though  carrying  a  strong  appearance  of  an 
immediate  exertion  of  Divine  energy,  lacks  by  a  hair's- 
breadth  the  quality  of  a  miracle.  For  the  wind  might  have 
arisen,  and  might  have  ceased,  in  the  ordinary  course  of 
Nature.  Hence  the  occurrence  did  not  "  compel  the  infer- 
ence of  extraordinary  Divine  agency."  In  like  manner  Mr. 
Mozley  considers  that  "the  appearance  of  the  cross  to 
Con stan tine  was  a  miracle,  or  a  special  providence,  ac- 
cording to  which  account  of  it  we  adopt.  As  only  a  mete- 
oric appearance  in  the  shape  of  a  cross  it  gave  some  token 
of  preternatural  agency,  but  not  full  evidence." 

In  the  Catholic  canton  of  Switzerland  where  I  now 
write,  and  still  more  among  the  pious  Tyrolese,  the  moun- 
tains are  dotted  with  shrines,  containing  offerings  of  all 
kinds,  in  acknowledgment  of  special  mercies — legs,  feet, 
arms,  and  hands  of  gold,  silver,  brass,  and  wood,  according 
as  worldly  possessions  enabled  the  grateful  heart  to  express 
its  indebtedness.  Most  of  these  offerings  are  made  to  the 
Virgin  Mary.  They  are  recognitions  of  "special  provi- 
dences," wrought  through  the  instrumentality  of  the  Mother 
of  God.  Mr.  Mozley's  belief,  that  of  the  Methodist  chron- 


MIRACLES  AND  SPECIAL  PROVIDENCES.  49 

icier,  and  that  of  the  Tyrolese  peasant,  are  substantially  the^ 
same.  Each  of  them  assumes  that  Nature,  instead  of  flow- 
ing ever  onward  in  the  uninterrupted  rhythm  of  cause  and 
effect,  is  mediately  ruled  by  the  free  human  will.  As  re- 
gards direct  action  upon  natural  phenomena,  man's  will  is 
confessedly  powerless,  but  it  is  the  trigger  which,  by  its 
own  free  action,  liberates  the  Divine  power.  In  this  sense, 
and  to  this  extent,  man,  of  course,  commands  Nature. 

Did  the  existence  of  this  belief  depend  solely  upon  the 
material  benefits  derived  from  it,  it  could  not,  in  my  opinion, 
last  a  decade.  As  a  purely  objective  fact  we  should  soon 
see  that  the  distribution  of  natural  phenomena  is  unaffected 
by  the  merits  or  the  demerits  of  man ;  that  the  law  of  gravi- 
tation crushes  the  simple  worshippers  of  Ottery  St.  Mary, 
while  singing  their  hymns,  just  as  surely  as  if  they  were 
engaged  in  a  midnight  brawl.  The  hold  of  this  belief  upon 
the  human  mind  is  not  due  to  outward  verification,  but  to 
the  inner  warmth,  force,  and  elevation  with  which  it  is  com- 
monly associated.  It  is  plain,  however,  that  these  feelings 
may  exist  under  the  most  various  forms.  They  are  not 
limited  to  Church  of  England  Protestantism — they  are  not 
even  limited  to  Christianity.  Though  less  refined,  they  are 
certainly  not  less  strong,  in  the  heart  of  the  Methodist  and 
the  Tyrolese  than  in  the  heart  of  Mr.  Mozley.  Indeed,  those 
feelings  belong  to  the  primal  powers  of  man's  nature.  A 
"  skeptic  "  may  have  them.  They  find  vent  in  the  battle- 
cry  of  the  Moslem.  They  take  hue  and  form  in  the  hunting- 
grounds  of  the  red  Indian ;  and  raise  all  of  them,  as  they 
raise  the  Christian,  upon  a  wave  of  victory,  above  the  ter- 
rors of  the  grave. 

The  character,  then,  of  a  miracle,  as  distinguished  from 
a  special  providence,  is  that  the  former  furnishes  proof, 
while  in  the  case  of  the  latter  we  have  only  surmise.  Dis- 
solve the  element  of  doubt,  and  the  alleged  fact  passes  from 
the  one  class  of  the  preternatural  into  the  other.  In  other 
3 


50  FRAGMENTS  OF  SCIENCE. 

words,  if  a  special  providence  could  be  proved  to  be  a  spe- 
cial providence,  it  would  cease  to  be  a  special  providence 
and  become  a  miracle.  There  is  not  the  least  cloudiness 
about  Mr.  Mozley's  meaning  here.  A  special  providence  is 
a  doubtful  miracle.  Why,  then,  not  use  the  correct  phra- 
seology ?  The  term  employed  conveys  no  negative  sug- 
gestion, whereas  the  negation  of  certainty  is  the  peculiar 
characteristic  of  the  thing  intended  to  be  expressed.  There 
is  an  apparent  unwillingness  on  the  part  of  Mr.  Mozley  to 
call  a  special  providence  what  his  own  definition  makes  it 
to  be.  Instead  of  speaking  of  it  as  a  doubtful  miracle,  he 
calls  it  "  an  invisible  miracle."  He  speaks  of  the  point  of 
contact  of  supernatural  power  with  the  chain  of  causation 
being  so  high  up  as  to  be  wiiolly,  or  in  part,  out  of  sight, 
whereas  the  essence  of  a  special  providence  is  the  uncer- 
tainty whether  there  is  any  contact  at  all,  either  high  or 
low.  By  the  use  of  an  incorrect  term,  however,  a  grave 
danger  is  avoided.  For  the  idea  of  doubt,  if  kept  system- 
atically before  the  mind,  would  soon  be  fatal  to  the  special 
providence  as  a  means  of  edification.  The  term  employed, 
on  the  contrary,  invites  and  encourages  the  trust  which  is 
necessary  to  supplement  the  evidence. 

This  inner  trust,  though  at  first  rejected  by  Mr.  Mozley 
in  favor  of  external  proof,  is  subsequently  called  upon  to 
do  momentous  duty  with  regard  to  miracles.  Whenever 
the  evidence  of  the  miraculous  seems  incommensurate  with 
the  fact  which  it  has  to  establish,  or  rather  when  the  fact 
is  so  amazing  that  hardly  any  evidence  is  sufficient  to  estab- 
lish it,  Mr.  Mozley  invokes  "the  affections."  They  must 
urge  the  reason  to  accept  the  conclusion  from  which  unaided 
it  recoils.  The  affections  and  emotions  are  eminently  the 
court  of  appeal  in  matters  of  real  religion,  which  is  an  affair 
of  the  heart,  but  they  are  not,  I  submit,  the  court  in  which 
to  weigh  allegations  regarding  the  credibility  of  physical 
facts.  These  must  be  judged  by  the  dry  light  of  the  intel- 


MIRACLES  AND   SPECIAL  PROVIDENCES.  51 

lect  alone,  appeals  to  the  affections  being  reserved  for  cases 
where  moral  elevation,  and  not  historic  conviction,  is  the 
aim.  It  is,  moreover,  because  the  result,  in  the  case  under 
consideration,  is  deemed  desirable  that  the  affections  are 
called  upon  to  back  it.  If  undesirable,  they  would,  with 
equal  right,  be  called  upon  to  act  the  other  way.  Even  to 
the  disciplined  scientific  mind  this  would  be  a  dangerous 
doctrine.  A  favorite  theory — the  desire  to  establish  or 
avoid  a  certain  result — can  so  warp  the  mind  as  to  destroy 
its  power  of  estimating  facts.  I  have  known  men  to  work 
for  years  under  a  fascination  of  this  kind,  unable  to  extri- 
cate themselves  from  its  fatal  influence.  They  had  certain 
data,  but  not,  as  it  happened,  enough.  By  a  process  exactly 
analogous  to  that  invoked  by  Mr.  Mozley  they  supplemented 
the  data,  and  went  wrong.  From  that  hour  their  intellects 
were  so  blinded  to  the  perception  of  adverse  phenomena 
that  they  never  reached  truth.  If,  then,  to  the  disciplined 
scientific  mind,  this  incongruous  mixture  of  proof  and  trust 
be  fraught  with  danger,  what  must  it  be  to  the  indiscrimi- 
nate audience  which  Mr.  Mozley  addresses  ?  In  calling 
upon  this  agency  he  acts  the  part  of  Frankenstein.  It  is 
the  monster  thus  evoked  that  we  see  stalking  abroad,  in 
the  so-called  spiritualistic  phenomena  of  the  present  day. 
Again,  I  say,  where  the  aim  is  to  elevate  the  mind,  to 
quicken  the  moral  sense,  to  kindle  the  fire  of  religion  in  the 
soul,  let  the  affections  by  all  means  be  invoked ;  but  they 
must  not  be  permitted  to  color  our  reports,  or  to  influence 
our  acceptance  of  reports  of  occurrences  in  external  Nature. 
Testimony  as  to  natural  facts  is  usually  worthless  when 
wrapped  in  this  atmosphere  of  the  affections,  the  most 
earnest  subjective  truth  being  thus  rendered  perfectly  com- 
patible with  the  most  astounding  objective  error. 

There  are  questions  in  judging  of  which  the  affections 
or  sympathies  are  often  our  best  guides,  the  estimation  of 
moral  goodness  being  one  of  these.  But  at  this  precise 


52  FRAGMENTS  OF  SCIENCE. 

point,  where  they  are  really  of  use,  Mr.  Mozley  excludes 
the  affections,  and  demands  a  miracle  as  a  certificate  of 
character.  He  will  not  accept  any  other  evidence  of  the 
perfect  goodness  of  Christ.  "  No  outward  life  or  conduct," 
he  says,  "  however  irreproachable,  could  prove  His  perfect 
sinlessness,  because  goodness  depends  upon  the  inward 
motive,  and  the  perfection  of  the  inward  motive  is  not 
proved  by  the  outward  act."  But  surely  the  miracle  is  an 
outward  act,  and  to  pass  from  it  to  the  inner  motive  im- 
poses a  greater  strain  upon  logic  than  that  involved  in  our 
ordinary  methods  of  estimating  men.  There  is,  at  least, 
moral  congruity  between  the  outward  goodness  and  the 
inner  life,  but  there  is  no  such  congruity  between  the  mira- 
cle and  the  life  within.  The  test  of  moral  goodness  laid 
down  by  Mr.  Mozley  is  not  the  test  of  John,  who  says,  "  He 
that  doeth  righteousness  is  righteous ; "  nor  is  it  the  test 
of  Jesus — "  By  their  fruits  ye  shall  know  them ;  do  men 
gather  grapes  of  thorns,  or  figs  of  thistles  ?  "  But  it  is  the 
test  of  another :  "  If  thou  be  the  Son  of  God,  command  that 
these  stones  be  made  bread."  For  my  own  part,  I  prefer 
the  attitude  of  Fichte  to  that  of  Mr.  Mozley.  "  The  Jesus 
of  John,"  says  this  noble  and  mighty  thinker,  "  knows  no 
other  God  than  the  True  God,  in  whom  we  all  are,  and  live, 
and  may  be  blessed,  and  out  of  whom  there  is  only  Death 
and  Nothingness.  And  he  appeals,  and  rightly  appeals,  in 
support  of  this  truth,  not  to  reasoning,  but  to  the  inward 
practical  sense  of  truth  in  man,  not  even  knowing  any  other 
proof  than  this  inward  testimony,  4  If  any  man  will  do  the 
will  of  Him  who  sent  me,  he  shall  know  of  the  doctrine 
whether  it  be  of  God." ' 

Accepting  Mr.  Mozley's  test,  with  which  alone  I  am  now 
dealing,  it  is  evident  that,  in  the  demonstration  of  moral 
goodness,  the  quantity  of  the  miraculous  comes  into  play. 
Had  Christ,  for  example,  limited  Himself  to  the  conversion 
of  water  into  wine,  He  would  have  fallen  short  of  the  per- 


MIRACLES  AND  SPECIAL  PROVIDENCES.  53 

formance  of  Jannes  and  Jambres,  for  it  is  a  smaller  thing  to 
convert  one  liquid  into  another  than  to  convert  a  dead  rod 
into  a  living  serpent.  But  Jannes  and  Jambres,  we  are  in- 
formed, were  not  good.  Hence,  if  Mr.  Mozley's  test  be  a 
true  one,  a  point  must  exist,  on  the  one  side,  of  which 
miraculous  power  demonstrates  goodness,  while  on  the  other 
side  it  does  not.  How  is  this  "  point  of  contrary  flexure  " 
to  be  determined?  It  must  lie  somewhere  between  the 
magicians  and  Moses,  for  within  this  space  the  power  passed 
from  the  diabolical  to  the  Divine.  But  how  to  mark  the 
point  of  passage — how,  out  of  a  purely  quantitative  differ- 
ence in  the  visible  manifestation  of  power  we  are  to  infer  a 
total  inversion  of  quality — it  is  extremely  difficult  to  see. 
Moses,  we  are  informed,  produced  a  large  reptile,  Jannes 
and  Jambres  produced  a  small  one.  I  do  not  possess  the 
intellectual  faculty  which  would  enable  me  to  infer  from 
those  data  either  the  goodness  of  the  one  or  the  badness  of 
the  other ;  and  in  the  highest  recorded  manifestations  of  the 
miraculous  I  am  equally  at  a  loss.  Let  us  not  play  fast  and 
loose  with  the  miraculous  ;  either  it  is  a  demonstration  of 
goodness  in  all  cases  or  in  none.  If  Mr.  Mozley  accepts 
Christ's  goodness  as  transcendent,  because  He  did  such 
works  as  no  other  man  did,  he  ought,  logically  speaking,  to 
accept  the  works  of  those  who,  in  His  name,  had  cast  out 
devils,  as  demonstrating  a  proportionate  goodness  on  their 
part.  But  it  is  people  of  this  class  who  are  consigned  to 
everlasting  fire  prepared  for  the  devil  and  his  angels.  Such 
zeal  as  that  of  Mr.  Mozley  for  miracles  tends,  I  fear,  to  eat 
his  religion  up.  The  logical  threatens  to  stifle  the  spiritual. 
The  truly  religious  soul  needs  no  miraculous  proof  of  the 
goodness  of  Christ.  The  words  addressed  to  Matthew  at 
the  receipt  of  custom  required  no  miracle  to  produce  obedi- 
ence. It  was  by  no  stroke  of  the  supernatural  that  Jesus 
caused  those  sent  to  seize  Him  to  go  backward  and  fall  to 
the  ground.  It  was  the  sublime  and  holy  effluence  from 


54  FRAGMENTS  OF  SCIENCE. 

within,  which  needed  no  prodigy  to  commend  it  to  the  rev- 
erence even  of  his  foes. 

As  regards  the  function  of  miracles  in  the  founding  of  a 
religion,  Mr.  Mozley  institutes  a  comparison  between  the 
religion  of  Christ  and  that  of  Mahomet,  and  he  derides  the 
latter  as  "  irrational "  because  it  does  not  profess  to  adduce 
miracles  in  proof  of  its  supernatural  origin.  But  the  re- 
ligion of  Mahomet,  notwithstanding  this  drawback,  has 
thriven  in  the  world,  and  at  one  time  it  held  sway  over 
larger  populations  than  Christianity  itself.  The  spread  and 
influence  of  Christianity  are,  however,  brought  forward  by 
Mr.  Mozley  as  "  a  permanent,  enormous,  and  incalculable 
practical  result"  of  Christian  miracles;  and  he  actually 
makes  use  of  this  result  to  strengthen  his  plea  for  the  mirac- 
ulous. His  logical  warrant  for  this  proceeding  is  not  clear. 
It  is  the  method  of  science,  when  a  phenomenon  presents 
itself,  to  the  production  of  which  several  elements  may  con- 
tribute, to  exclude  them  one  by  one,  so  as  to  arrive  at 
length  at  the  truly  effective  cause.  Heat,  for  example,  is 
associated  with  a  phenomenon ;  we  exclude  heat,  but  the 
phenomenon  remains :  hence,  heat  is  not  its  cause.  Mag- 
netism is  associated  with  a  phenomenon ;  we  exclude  mag- 
netism, but  the  phenomenon  remains :  hence,  magnetism  is 
not  its  cause.  Thus,  also,  when  we  seek  the  cause  of  the 
diffusion  of  a  religion — whether  it  be  due  to  miracles  or  to 
the  spiritual  force  of  its  founders — we  exclude  the  miracles, 
and,  finding  the  result  unchanged,  we  infer  that  miracles 
are  not  the  effective  cause.  This  important  experiment 
Mahometanism  has  made  for  us.  It  has  lived  and  spread 
without  miracles ;  and  to  assert,  in  the  face  of  this,  that 
Christianity  has  spread  because  of  miracles,  is  not  more  op- 
posed to  the  spirit  of  science  than  to  the  common-sense  of 
mankind. 

The  incongruity  of  inferring  moral  goodness  from  mirac- 
ulous power  has  been  dwelt  upon  above ;  in  another  par- 


MIRACLES  AND  SPECIAL  PROVIDENCES.  55 

ticular  also  the  strain  put  upon  miracles  by  Mr.  Mozley  is, 
I  think,  more  than  they  can  bear.  In  consistency  with  his 
principles,  it  is  difficult  to  see  how  he  is  to  draw  from  the 
miracles  of  Christ  any  certain  conclusion  as  to  His  Divine 
nature.  He  dwells  very  forcibly  on  what  he  calls  "  the  argu- 
ment from  experience,"  in  the  demolition  of  which  he  takes 
evident  delight.  He  destroys  the  argument,  and  repeats  it 
for  the  mere  pleasure  of  again  and  again  knocking  the 
breath  out  of  it.  Experience,  he  urges,  can  only  deal  with 
the  past ;  and  the  moment  we  attempt  to  project  experience 
a  hair's  breadth  beyond  the  point  it  has  at  any  moment 
reached,  we  are  condemned  by  reason.  It  appears  to  me 
that,  when  he  infers  from  Christ's  miracles  a  divine  and 
altogether  superhuman  energy,  Mr.  Mozley  places  himself 
precisely  under  this  condemnation.  For  what  is  his  logical 
ground  for  concluding  that  the  miracles  of  the  New  Testa- 
ment illustrate  Divine  power  ?  May  they  not  be  the  result 
of  expanded  human  power  ?  A  miracle  he  defines  as  some- 
thing impossible  to  man.  But  how  does  he  know  that  the 
miracles  of  the  New  Testament  are  impossible  to  man  ? 
Seek  as  he  may,  he  has  absolutely  no  reason  to  adduce  save 
this — that  man  has  never  hitherto  accomplished  such  things. 
But  does  the  fact  that  man  has  never  raised  the  dead  prove 
that  he  can  never  raise  the  dead  ?  "  Assuredly  not,"  must 
be  Mr.  Mozley's  reply ;  "  for  this  would  be  pushing  experi- 
ence beyond  the  limit  it  has  now  reached — which  I  pro- 
nounce unlawful."  Then  a  period  may  come  when  man 
will  be  able  to  raise  the  dead.  If  this  be  conceded — and  I 
do  not  see  how  Mr.  Mozley  can  avoid  the  concession — it 
destroys  the  necessity  of  inferring  Christ's  divinity  from  his 
miracles.  He,  it  may  be  contended,  antedated  the  humanity 
of  the  future ;  as  a  mighty  tidal-wave  leaves  high  upon  the 
beach  a  mark  which  by-and-by  becomes  the  general  level 
of  the  ocean.  Turn  the  matter  as  you  will,  no  other  warrant 
will  be  found  for  the  all-important  conclusion  that  Christ's 


56  FRAGMENTS  OF  SCIENCE. 

miracles  demonstrate  Divine  power,  than  an  argument 
which  has  been  stigmatized  by  Mr.  Mozley  as  "  a  rope  of 
sand  " — the  argument  from  experience. 

The  learned  Bampton  Lecturer  would  be  in  this  posi- 
tion even  if  he  had  seen  with  his  own  eyes  every  miracle 
recorded  in  the  New  Testament.  But  he  has  not  seen  these 
miracles;  and  his  intellectual  plight  is,  therefore,  worse. 
He  accepts  these  miracles  on  testimony.  Why  does  he  be- 
lieve that  testimony  ?  How  does  he  know  that  it  is  not 
delusion ;  how  is  he  sure  that  it  is  not  even  falsehood  ? 
He  will  answer  that  the  writing  bears  the  marks  of  sobriety 
and  truth ;  and  that,  in  many  cases,  the  bearers  of  this  mes- 
sage to  mankind  sealed  it  with  their  blood.  Granted  with 
all  my  heart ;  but  whence  the  value  of  all  this  ?  Is  it  not 
solely  derived  from  the  fact  that  men,  as  we  know  them,  do 
not  sacrifice  their  lives  in  the  attestation  of  that  which  they 
know  to  be  untrue  ?  Does  not  the  entire  value  of  the  tes- 
timony of  the  apostles  depend  ultimately  upon  our  expe- 
rience of  human  nature  ?  It  appears,  therefore,  that  those 
who  alleged  to  have  seen  the  miracles  based  their  inferences 
from  what  they  saw  on  the  argument  from  experience ;  and 
that  Mr.  Mozley  bases  his  belief  in  their  testimony  on  the 
same  argument.  The  weakness  of  his  conclusion  is  aug- 
mented by  this  double  insertion  of  a  principle  of  belief  to 
which  he  flatly  denies  rationality.  His  reasoning,  in  fact, 
cuts  two  ways — if  it  destroys  our  trust  in  the  order  of  Na- 
ture, it  far  more  effectually  abolishes  the  basis  on  which 
Mr.  Mozley  seeks  to  found  the  Christian  religion. 

Over  this  argument  from  experience,  which,  at  bottom, 
is  his  argument,  Mr.  Mozley  rides  rough-shod.  There  is  a 
dash  of  scorn  in  the  energy  with  which  he  tramples  on  it. 
Probably  some  previous  writer  had  made  too  much  of  it, 
and  thus  invited  his  powerful  assault.  Finding  the  diffi- 
culty of  belief  in  miracles  to  arise  from  their  being  in  con- 
tradiction to  the  order  of  Nature,  he  set  himself  to  examine 


MIRACLES  AND  SPECIAL  PROVIDENCES.  57 

the  grounds  of  our  belief  in  that  order.  With  a  vigor  of 
logic  rarely  equalled,  and  with  a  confidence  in  its  conclu- 
sions never  surpassed,  he  disposes  of  this  belief  in  a  manner 
calculated  to  startle  those  who,  without  due  examination, 
had  come  to  the  conclusion  that  the  order  of  Nature  was 
secure. 

What  we  mean,  he  says,  by  our  belief  in  the  order  of 
Nature,  is  the  belief  that  the  future  will  be  like  the  past. 
There  is  not,  according  to  Mr.  Mozley,  the  slightest  rational 
basis  for  this  belief. 

"  That  any  cause  in  Nature  is  more  permanent  than  its  existing  and 
known  effects,  extending  further,  and  about  to  produce  other  and  more 
instances  besides  what  it  has  produced  already,  we  have  no  evidence. 
Let  us  imagine,"  he  continues,  "  the  occurrence  of  a  particular  physical 
phenomenon  for  the  first  time.  Upon  that  single  occurrence  we  should 
have  but  the  very  faintest  expectation  of  another.  If  it  did  occur  again, 
once  or  twice,  so  far  from  counting  on  another  occurrence,  a  cessation 
would  occur  as  the  most  natural  event  to  us.  But  let  it  continue  one 
hundred  times,  and  we  should  find  no  hesitation  in  inviting  persons  from 
a  distance  to  see  it ;  and  if  it  occurred  every  day  for  years,  its  occur- 
rence would  be  a  certainty  to  us,  its  cessation  a  marvel.  .  .  .  What 
ground  of  reason  can  we  assign  for  an  expectation  that  any  part  of  the 
course  of  Nature  will  be  the  next  moment  what  it  has  been  up  to  this 
moment,  i.  e.,  for  our  belief  in  the  uniformity  of  Nature  ?  None.  No 
demonstrative  reason  can  be  given,  for  the  contrary  to  the  recurrence  of 
a  fact  of  Nature  is  no  contradiction.  No  probable  reason  can  be  given, 
for  all  probable  reasoning  respecting  the  course  of  Nature  is  founded  upon 
this  presumption  of  likeness,  and,  therefore,  cannot  be  the  foundation 
of  it.  No  reason  can  be  given  for  this  belief.  It  is  without  a  reason. 
It  rests  upon  no  rational  grounds,  and  can  be  traced  to  no  rational  prin- 
ciple." 

"  Every  thing,"  Mr.  Mozley,  however,  adds,  "  depends 
upon  this  belief,  every  provision  we  make  for  the  future, 
every  safeguard  and  caution  we  employ  against  it,  all  cal- 
culation, all  adjustment  of  means  to  ends  supposes  this  be- 
lief; and  yet  this  belief  has  no  more  producible  reason  for 
it  than  a  speculation  of  fancy.  ...  It  is  necessary,  all-im- 


58  FKAGMENTS  OF  SCIENCE. 

portant  for  the  purposes  of  life,  but  solely  practical,  and 
possesses  no  intellectual  character.  .  .  .  The  proper  func- 
tion," continues  Mr.  Mozley,  "  of  the  inductive  principle, 
the  argument  from  experience,  the  belief  in  the  order  of 
Nature — by  whatever  phrase  we  designate  the  same  instinct 
— is  to  operate  as  a  practical  basis  for  the  affairs  of  life  and 
the  carrying  on  of  human  society."  To  sum  up,  the  belief 
in  the  order  of  Nature  is  general,  but  it  is  "  an  unintelligent 
impulse,  of  which  we  can  give  no  rational  account."  It  is 
inserted  in  our  constitution  solely  to  induce  us  to  till  our 
fields,  to  raise  our  winter  fuel,  and  thus  to  meet  the  future 
on  the  perfectly  gratuitous  supposition  that  that  future  will 
be  like  the  past. 

"  Thus,  step  by  step,"  says  Mr.  Mozley,  with  the  empha- 
sis of  a  man  who  feels  his  position  to  be  a  strong  one,  "  has 
philosophy  loosened  the  connection  of  the  order  of  Nature 
with  the  ground  of  reason,  befriending  in  exact  proportion 
as  it  has  done  this  the  principle  of  miracles."  For  "  this 
belief,  not  having  itself  a  foundation  in  reason,  the  ground 
is  gone  upon  which  it  could  be  maintained  that  miracles, 
as  opposed  to  the  order  of  Nature,  are  opposed  to  reason." 
When  we  regard  this  belief  in  connection  with  science,  "  in 
which  connection  it  receives  a  more  imposing  name,  and  is 
called  the  inductive  principle,"  the  result  is  the  same. 
"  The  inductive  principle  is  only  this  unreasoning  impulse 
applied  to  a  scientifically  ascertained  fact.  .  .  .  Science  has 
led  up  to  the  fact,  but  there  it  stops,  and  for  converting 
this  fact  into  a  law  a  totally  unscientific  principle  comes 
into  play,  the  same  as  that  which  generalizes  the  common- 
est observation  of  Nature." 

The  eloquent  pleader  of  the  cause  of  miracles  passes 
over  without  a  word  the  results  of  scientific  investigation 
as  proving  any  thing  rational  regarding  the  principles  or 
methods  by  which  such  results  have  been  achieved.  Here, 
as  before,  he  declines  the  test,  "  By  their  fruits  shall  ye 


MIRACLES  AND   SPECIAL  PROVIDENCES.  59 

know  them."  Perhaps  the  best  way  of  proceeding  will  be 
to  give  one  or  two  examples  of  the  mode  in  which  men  of 
science  apply  the  unintelligent  impulse  with  which  Mr. 
Mozley  credits  them,  and  which  shall  show  by  illustration 
the  surreptitious  character  of  the  method  by  which  they 
climb  from  the  region  of  facts  to  that  of  laws. 

It  was  known  before  the  sixteenth  century  that,  the  end 
of  an  open  tube  being  dipped  into  water,  on  drawing  an 
air-tight  piston  up  the  tube  the  water  follows  the  piston, 
and  this  fact  had  been  turned  to  account  in  the  construction 
of  the  common  pump.  The  effect  was  explained  at  the 
time  by  the  maxim,  "  Nature  abhors  a  vacuum."  It  was 
not  known  that  there  was  any  limit  to  the  height  to  which 
the  water  would  ascend,  until,  on  one  occasion,  the  garden- 
ers of  Florence,  while  attempting  to  raise  the  water  a  very 
great  elevation,  found  that  the  column  ceased  at  a  height 
of  thirty-two  feet.  Beyond  this  all  the  skill  of  the  pump- 
maker  could  not  get  it  to  rise.  The  fact  was  brought  to 
the  notice  of  Galileo,  and  he,  soured  by  a  world  which  had 
not  treated  his  science  over-kindly,  is  said  to  have  twitted 
the  philosophy  of  the  time  by  remarking  that  Nature  evi- 
dently abhorred  a  vacuum  only  to  a  height  of  thirty-two 
feet.  But  Galileo  did  not  solve  the  problem.  It  was  taken 
up  by  his  pupil  Torricelli,  who  pondered  it,  and  while  he 
did  so  various  thoughts  regarding  it  arose  in  his  mind.  It 
occurred  to  him  that  the  water  might  be  forced  up  in  the 
tube  by  a  pressure  applied  to'the  surface  of  the  water  out- 
side. But  where,  under  the  actual  circumstances,  was  such 
a  pressure  to  be  found  ?  After  much  reflection,  it  flashed 
upon  Torricelli  that  the  atmosphere  might  possibly  exert 
the  pressure ;  that  the  impalpable  air  might  possess  weight, 
and  that  a  column  of  water  thirty-two  feet  high  might  be 
of  the  exact  weight  necessary  to  hold  the  pressure  of  the 
atmosphere  in  equilibrium. 

There  is  much  in  this   process  of  pondering   and   its 


60  FRAGMENTS  OF  SCIENCE. 

results  which  it  is  impossible  to  analyze.  It  is  by  a  kind  of 
inspiration  that  we  rise  from  the  wise  and  sedulous  con- 
templation of  facts  to  the  principles  on  which  they  depend. 
The  mind  is,  as  it  were,  a  photographic  plate,  which  is 
gradually  cleansed  by  the  effort  to  think  rightly,  and  which 
when  so  cleansed,  and  not  before,  receives  impressions  from 
the  light  of  truth.  This  passage  from  facts  to  principles  is 
called  induction,  which  in  its  highest  form  is  inspiration ; 
but,  to  make  it  sure,  the  inward  sight  must  be  shown 
to  be  in  accordance  with  outward  fact.  To  prove  or  dis- 
prove the  induction,  we  must  resort  to  deduction  and  ex- 
periment. 

Torricelli  reasoned  thus  :  If  a  column  of  water  thirty- 
two  feet  high  holds  the  pressure  of  the  atmosphere  in 
equilibrium,  a  shorter  column  of  a  heavier  liquid  ought  to 
do  the  same.  Now,  mercury  is  thirteen  times  heavier  than 
water ;  hence,  if  my  induction  be  correct,  the  atmosphere 
ought  to  be  able  to  sustain  only  thirty  inches  of  mercury. 
Here,  then,  is  a  deduction  which  can  be  immediately  sub- 
mitted to  experiment.  Torricelli  took  a  glass  tube  a  yard 
or  so  in  length,  closed  at  one  end  and  open  at  the  other, 
and  filling  it  with  mercury,  he  stopped  the  open  end  with 
his  thumb,  and  inverted  it  in  a  basin  filled  with  the  liquid 
metal.  One  can  imagine  the  feeling  with  which  Torricelli 
removed  his  thumb,,  and  the  delight  he  experienced  when 
he  found  that  his  thought  had  forestalled  a  fact  never  before 
revealed  to  human  eyes.  The  column  sank,  but  ceased  to 
sink  at  a  height  of  thirty  inches,  leaving  the  Torricellian 
vacuum  overhead.  From  that  hour  the  theory  of  the  pump 
was  established. 

The  celebrated  %  Pascal  followed  Torricelli  with  a  still 
further  deduction.  He  reasoned  thus :  If  the  mercurial 
column  be  supported  by  the  atmosphere,  the  higher  we 
ascend  in  the  air  the  lower  the  column  ought  to  sink,  for 
the  less  will  be  the  weight  of  the  air  overhead.  He  ascend- 


MIRACLES  AND  SPECIAL  PROVIDENCES.  61 

ed  the  Puy  de  Dome,  carrying  with  him  a  barometric 
column,  and  found  that  as  he  ascended  the  mountain  the 
column  sank,  and  that  as  he  descended  the  column  rose. 

Between  the  time  here  referred  to  and  the  present, 
millions  of  experiments  have  been  made  upon  this  subject. 
Every  village  pump  is  an  apparatus  for  such  experiments. 
In  thousands  of  instances,  moreover,  pumps  have  refused 
to  work ;  but  on  examination  it  has  infallibly  been  found 
that  the  well  was  dry,  that  the  pump  required  priming,  or 
that  some  other  defect  in  the  apparatus  accounted  for  the 
anomalous  action.  In  every  case  of  the  kind  the  skill  of 
the  pump-maker  has  been  found  to  be  the  true  remedy.  In 
no  case  has  the  pressure  of  the  atmosphere  ceased ;  con- 
stancy, as  regards  the  lifting  of  pump-water,  has  been 
hitherto  the  demonstrated  rule  of  Nature.  So  also  as  regards 
Pascal's  experiment.  His  experience  has  been  the  universal 
experience  ever  since.  Men  have  climbed  mountains,  and 
gone  up  in  balloons ;  but  no  deviation  from  Pascal's  result 
has  ever  been  observed.  Barometers,  like  pumps,  have 
refused  to  act;  but  instead  of  indicating  any  suspension  of 
the  operations  of  Nature,  or  any  interference  on  the  part  of 
its  Author  with  atmospheric  pressure,  examination  has  in 
every  instance  fixed  the  anomaly  upon  the  instruments 
themselves.  It  is  this  welding,  then,  of  rigid  logic  to  veri- 
fying fact  that  Mr.  Mozley  refers  to  an  "  unreasoning  im- 
pulse." 

Let  us  now  briefly  consider  the  case  of  Newton.  Before 
his  time  men  had  occupied  themselves  with  the  problem  of 
the  solar  system.  Kepler  had  deduced,  from  a  vast  mass 
of  observations,  the  general  expressions  of  planetary  motion 
known  as  "  Kepler's  laws."  It  had  b,een  observed  that  a 
magnet  attracts  iron  ;  and  by  one  of  those  flashes  of  inspi- 
ration which  reveal  to  the  human  mind  the  vast  in  the 
minute,  the  general  in  the  particular,  it  occurred  to  Kepler, 
that  the  force  by  which  bodies  fall  to  the  earth  might  also 


62  FRAGMENTS  OF  SCIENCE. 

be  an  attraction.  Newton  pondered  all  these  things.  He 
had  a  great  power  of  pondering.  He  could  look  into  the 
darkest  subject  until  it  became  entirely  luminous.  How 
this  light  arises  we  cannot  explain ;  but,  as  a  matter  of 
fact,  it  does  arise.  Let  me  remark  here,  that  this  power  of 
pondering  facts  is  one  with  which  the  ancients  could  be 
but  imperfectly  acquainted.  They  found  the  uncontrolled 
exercise  of  the  imagination  too  pleasant  to  expend  much 
time  in  gathering  and  brooding  over  facts.  Hence  it  is  that 
when  those  whose  education  has  been  derived  from  the 
ancients  speak  of  "  the  reason  of  man,"  they  are  apt  to 
omit  from  their  conception  of  reason  one  of  its  greatest 
powers.  "Well,  Newton  slowly  marshalled  his  thoughts,  or 
rather  they  came  to  him  while  he  "intended  his  mind," 
rising  one  after  another  like  a  series  of  intellectual  births 
out  of  chaos.  He  made  this  idea  of  attraction  his  own. 
But  to  apply  the  idea  to  the  solar  system,  it  was  necessary 
to  know  the  magnitude  of  the  attraction  and  the  law  of  its 
variation  with  the  distance.  His  conceptions  first  of  all 
passed  from  the  action  of  the  earth  as  a  whole,  to  that  of 
its  constituents  particles,  the  integration  of  which  composes 
the  whole.  And  persistent  thought  brought  more  and 
more  clearly  out  the  final  divination,  that  every  particle  of 
matter  attracts  every  other  particle  by  a  force  which  varies 
inversely  as  the  square  of  the  distance  between  the  par- 
ticles. This  is  Newton's  celebrated  law  of  inverse  squares. 
Here  we  have  the  flower  and  outcome  of  his  induction  ;  and 
how  to  verify  it,  or  to  disprove  it,  was  the  next  question. 
The  first  step  of  Newton  in  this  direction  was  to  prove, 
mathematically,  that  if  this  law  of  attraction  be  the  true 
one ;  if  the  earth  be  constituted  of  particles  which  obey 
this  law ;  then  the  action  of  a  sphere  equal  to  the  earth  in 
size  on  a  body  outside  of  it,  is  the  same  as  that  which 
would  be  exerted  if  the  whole  mass  of  the  sphere  were 
contracted  to  a  point  at  its  centre.  Practically  speaking, 


MIRACLES  AND  SPECIAL  PROVIDENCES.  63 

then,  the  centre  of  the  earth  is  the  point  from  which 
distances  must  be  measured  to  bodies  attracted  by  the 
earth.  This  was  the  first-fruit  of  his  deduction. 

From  experiments  executed  before  his  time,  Newton 
knew  the  amount  of  the  earth's  attraction  at  the  earth's  sur- 
face, or  at  a  distance  of  4,000  miles  from  its  centre.  His 
object  now  was  to  measure  the  attraction  at  a  greater  dis- 
tance, and  thus  to  determine  the  law  of  its  diminution. 
But  how  was  he  to  find  a  body  at  a  sufficient  distance  ? 
He  had  no  balloon,  and  even  if  had,  he  knew  that  any  height 
which  he  could  attain  would  be  too  small  to  enable  him  to 
solve  his  problem.  What  did  he  do  ?  He  fixed  his  thoughts 
upon  the  moon — a  body  at  a  distance  of  240,000  miles,  or 
sixty  times  the  earth's  radius  from  the  earth's  centre.  He 
virtually  weighed  the  moon,  and  found  that  weight  to  be 
3-gVo^h  of  what  it  would  be  at  the  earth's  surface.  This  is 
exactly  what  his  theory  required.  I  will  not  dwell  here  upon 
the  pause  of  Newton  after  his  first  calculations,  or  speak  of 
his  self-denial  in  withholding  them,  because  they  did  not 
quite  agree  with  the  observations  then  at  his  command. 
Newton's  action  in  this  matter  is  the  normal  action  of  the 
scientific  mind.  If  it  were  otherwise — if  scientific  men  were 
not  accustomed  to  demand  verification — if  they  were  satis- 
fied with  the  imperfect  while  the  perfect  is  attainable,  their 
science,  instead  of  being,  as  it  is,  a  fortress  of  adamant, 
would  be  a  house  of  clay,  ill-fitted  to  bear  the  buffetings  of 
the  theologic  storms  to  which  it  has  been  from  time  to  time, 
and  is  at  present  exposed. 

Thus,  we  see,  that  Newton,  like  Torricelli,  first  pondered 
his  facts,  illuminated  them  with  persistent  thought,  and 
finally  divined  the  character  of  the  force  of  gravitation.  But 
having  thus  travelled  inward  to  the  principle,  he  had  to  re- 
verse his  steps,  carry  the  principle  outward,  and  justify  it 
by  demonstrating  its  fitness  to  external  Nature.  This  he 
did  by  determining  the  attraction  of  the  earth  and  moon. 


64  FRAGMENTS  OF  SCIENCE. 

And  here,  in  passing,  I  would  notice  a  point  which  is 
well  worthy  of  attention.  Kepler  had  deduced  his  laws 
from  observation.  As  far  back  as  those  observations  ex- 
tended, the  planetary  motions  had  obeyed  these  laws  ;  and, 
neither  Kepler  nor  Newton  entertained  a  doubt  as  to  their 
continuing  to  obey  them.  Year  after  year,  as  the  ages 
rolled,  they  believed  that  those  laws  would  continue  to 
illustrate  themselves  in  the  heavens.  But  this  was  not  suf- 
ficient. The  scientific  mind  can  find  no  repose  in  the  mere 
registration  of  sequence  in  Nature.  The  further  question 
intrudes  itself  with  resistless  might :  whence  comes  the  se- 
quence ?  What  is  it  that  binds  the  consequent  with  its  an- 
tecedent in  Nature  ?  The  truly  scientific  intellect  never  can 
attain  rest  until  it  reaches  the  forces  by  which  the  observed 
succession  is  produced.  It  was  thus  with  Torricelli ;  it  was 
thus  with  Newton ;  it  is  thus  preeminently  with  the  real 
scientific  man  of  to-day.  In  common  with  the  most  igno- 
mnt,  he  shares  the  belief  that  spring  will  succeed  winter, 
that  summer  will  succeed  spring,  that  autumn  will  succeed 
summer,  and  that  winter  will  succeed  autumn.  But  he 
knows  still  further — and  this  knowledge  is  essential  to  his 
intellectual  repose — that  this  succession,  besides  being  per- 
manent, is,  under  the  circumstances,  necessary  •  that  the 
gravitating  force  exerted  between  the  sun,  and  a  revolving 
sphere  with  an  axis  inclined  to  the  plane  of  its  orbit,  must 
produce  the  observed  succession  of  the  seasons.  Not  until 
this  relation  between  forces  and  phenomena  has  been  es- 
tablished is  the  law  of  reason  rendered  concentric  with  the 
law  of  Nature,  and  not  until  this  is  effected  does  the  mind 
of  the  scientific  philosopher  rest  in  peace. 

The  expectation  of  likeness,  then,  in  the  procession  of 
phenomena  is  not  that  on  which  the  scientific  mind  founds 
its  belief  in  the  order  of  Nature.  If  the  force  be  permanent 
the  phenomena  are  necessary,  whether  they  resemble  or  do 
not  resemble  any  thing  that  has  gone  before.  Hence,  in 


MIRACLES  AND  SPECIAL  PROVIDENCES.  65 

judging  of  the  order  of  Nature,  our  inquiries  eventually 
relate  to  the  permanence  of  force.  From  Galileo  to  Newton, 
from  Newton  to  our  own  time,  eager  eyes  have  been  scan- 
ning the  heavens,  and  clear  heads  have  been  pondering  the 
phenomena  of  the  solar  system.  The  same  eyes  and  minds 
have  been  also  observing,  experimenting,  and  reflecting  on 
the  action  of  gravity  at  the  surface  of  the  earth.  Nothing 
has  occurred  to  indicate  that  the  operation  of  the  law  has 
for  a  moment  been  suspended ;  nothing  has  ever  intimated 
that  Nature  has  been  crossed  by  spontaneous  action,  or 
that  a  state  of  things  at  any  time  existed  which  could  not 
be  rigorously  deduced  from  the  preceding  state.  Given  the 
distribution  of  matter  and  the  forces  in  operation  in  the 
time  of  Galileo,  the  competent  mathematician  of  that  day 
could  predict  what  is  now  occurring  in  our  own.  We  cal- 
culate eclipses  before  they  have  occurred,  and  find  them 
true  to  the  second.  We  determine  the  dates  of  those  that 
have  occurred  in  the  early  times  of  history,  and  find  calcu- 
lations and  history  at  peace.  Anomalies  and  perturba- 
tions in  the  planets  have  been  over  and  over  again  observed, 
but  these,  instead  of  demonstrating  any  inconstancy  on  the 
part  of  natural  law,  have  invariably  been  reduced  to  conse- 
quences of  that  law.  Instead  of  referring  the  perturba- 
tions of  Uranus  to  any  interference  on  the  part  of  the 
Author  of  Nature  with  the  law  of  gravitation,  the  question 
which  the  astronomer  proposed  to  himself  was,  "  How,  in 
accordance  with  this  law,  can  the  perturbation  be  pro- 
duced ?  "  Guided  by  a  principle,  he  was  enabled  to  fix  the 
point  of  space  in  which,  if  a  mass  of  matter  were  placed, 
the  observed  perturbations  would  follow.  We  know  the 
result.  The  practical  astronomer  turned  his  telescope  tow- 
ard the  region  which  the  intellect  of  the  theoretic  astrono- 
mer had  already  explored,  and  the  planet  now  named 
Neptune  was  found  in  its  predicted  place.  A  very  re- 
spectable outcome,  it  will  be  admitted,  of  an  impulse  which 


66  FRAGMENTS  OF  SCIENCE. 

"  rests  upon  no  rational  grounds,  and  can  be  traced  to  no 
rational  principle  ;  "  which  possesses  "  no  intellectual  char- 
acter;" which  "philosophy"  has  uprooted  from  "the 
ground  of  reason,"  and  fixed  in  that  "  large  irrational  de- 
partment "  discovered  for  it  by  Mr.  Mozley,  in  the  hitherto 
unexplored  wildernesses  of  the  human  mind. 

The  proper  function  of  the  inductive  principle,  or  the 
-belief  in  the  order  of  Nature,  says  Mr.  Mozley,  is  "  to  act 
as  a  practical  basis  for  the  affairs  of  life,  and  the  carrying 
on  of  human  society."  But  what,  it  may  be  asked,  has  the 
planet  Neptune,  or  the  belts  of  Jupiter,  or  the  whiteness 
about  the  poles  of  Mars,  to  do  with  the  affairs  of  society  ? 
How  is  society  affected  by  the  fact  that  the  sun's  atmos- 
phere contains  sodium,  or  that  the  nebula  of  Orion  contains 
hydrogen  gas  ?  Nineteen-twentieths  of  the  force  employed 
in  the  exercise  of  the  inductive  principle,  which,  reiterates 
Mr.  Mozley,  is  "purely  practical,"  have  been  expended  upon 
subjects  as  unpractical  as  these.  What  practical  interest 
has  society  in  the  fact  that  the  spots  on  the  sun  have  a 
decennial  period,  and  that  when  a  magnet  is  closely 
watched  for  half  a  century,  it  is  found  to  perform  small 
motions  which  synchronize  with  the  appearance  and  disap- 
pearance of  the  solar  spots  ?  And  yet,  I  doubt  not,  Sir 
Edward  Sabine  would  deem  a  life  of  intellectual  toil  amply 
rewarded  by  being  privileged  to  solve,  at  its  close,  these 
infinitesimal  motions. 

The  inductive  principle  is  founded  in  man's  desire  to 
know — a  desire  arising  from  his  position  among  phenom- 
ena which  are  reducible  to  order  by  his  intellect.  The 
material  universe  is  the  complement  of  the  intellect,  and 
without  the  study  of  its  laws  reason  would  never  have 
awoke  to  its  higher  forms  of  self-consciousness  at  all.  It 
is  the  non-ego,  through  and  by  which  the  ego  is  endowed 
with  self-discernment.  We  hold  it  to  be  an  exercise  of 
reason  to  explore  the  meaning  of  a  universe  to  which  we 


MIRACLES  AND  SPECIAL  PROVIDENCES.  67 

stand  in  this  relation,  and  the  work  we  have  accomplished 
is  the  proper  commentary  on  the  methods  we  have  pursued. 
Before  these  methods  were  adopted  the  unbridled  imagi- 
nation roamed  through  Nature,  putting  in  the  place  of 
law  the  figments  of  superstitious  dread.  For  thousands  of 
years  witchcraft,  and  magic,  and  miracles,  and  special  provi- 
dences, and  Mr.  Mozley's  "  distinctive  reason  of  man,"  had 
the  world  to  themselves.  They  made  worse  than  nothing 
of  it — worse,  I  say,  because  they  let  and  hindered  those 
who  might  have  made  something  of  it.  Hence  it  is  that 
during  a  single  lifetime  of  this  era  of  "  unintelligent  im- 
pulse," the  progress  in  natural  knowledge  is  all  but  infinite 
as  compared  with  that  of  the  ages  which  preceded  ours. 

The  believers  in  magic  and  miracles  of  a  couple  of 
centuries  ago  had  all  the  strength  of  Mr.  Mozley's  present 
logic  on  their  side.  They  had  done  for  themselves  what 
he  rejoices  in  having  so  effectually  done  for  us — cleared  the 
ground  of  the  belief  in  the  order  of  Nature,  and  declared 
magic,  miracles,  and  witchcraft,  to  be  matters  for  ordinary 
evidence  to  decide.  "The  principle  of  miracles"  thus 
"  befriended "  had  free  scope,  and  we  know  the  result. 
Lacking  that  rock-barrier  of  natural  knowledge  which  we, 
laymen  of  England,  now  possess,  keen  jurists  and  cultivated 
men  were  hurried  on  to  deeds,  the  bare  recital  of  which 
makes  the  blood  run  cold.  Skilled  in  all  the  rules  of  human 
evidence,  and  versed  in  all  the  arts  of  cross-examination, 
these  men,  nevertheless,  went  systematically  astray,  and 
committed  the  deadliest  wrongs  against  humanity.  And 
why  ?  Because  they  could  not  put  Nature  into  the  witness- 
box,  and  question  her ;  of  her  voiceless  "  testimony  "  they 
knew  nothing.  In  all  cases  between  man  and  man,  their 
judgment  was  to  be  relied  on ;  but  in  all  cases  between 
man  and  Nature  they  were  blind  leaders  of  the  blind.1 

1  "  In  1664  two  women  were  hung  in  Suffolk,  under  a  sentence  of  Sir 
Matthew  Hale,  who  took  the  opportunity  of  declaring  that  the  reality  of 


68  FRAGMENTS  OF  SCIENCE. 

Mr.  Mozley  concedes  that  it  would  be  no  great  result 
for  miracles  to  be  accepted  by  the  ignorant  and  superstitious, 
"  because  it  is  easy  to  satisfy  those  who  do  not  inquire." 
But  he  does  consider  it  "  a  great  result "  that  they  have 
been  accepted  by  the  educated.  In  what  sense  educated  ? 
Like  those  statesmen,  jurists,  and  church  dignitaries  whose 
education  was  unable  to  save  them  from  the  frightful  errors 
glanced  at  above?  Not  even  in  this  sense;  for  the  great 
mass  of  Mr.  Mozley's  educated  people  had  no  legal  training, 
and  must  have  been  absolutely  defenceless  against  delusions 
which  could  set  even  that  training  at  naught.  Like  nine- 
tenths  of  our  clergy  at  the  present  day,  they  were  versed  in 
the  literature  of  Greece,  Borne,  and  Judea  ;  but  as  regards 
a  knowledge  of  Nature,  which  is  here  the  one  thing  needful, 
they  were  "  noble  savages,"  and  nothing  more.  In  the 
case  of  miracles,  then,  it  behooves  us  to  understand  the 
weight  of  the  negative,  before  we  assign  a  value  to  the 
positive ;  to  comprehend  the  protest  of  Nature  before  we 
attempt  to  measure,  with  it,  the  assertions  of  men.  We 
have  only  to  open  our  eyes  to  see  what  honest,  and  even 
intellectual,  men  and  women  are  capable  of  in  the  way  of 
evidence  in  this  nineteenth  century  of  the  Christian  era, 
and  in  latitude  fifty-two  degrees  north.  The  experience 
thus  gained  ought,  I  imagine,  to  influence  our  opinion 
regarding  the  testimony  of  people  inhabiting  a  sunnier 
clime,  with  a  richer  imagination,  and  without  a  particle  of 
that  restraint  which  the  discoveries  of  physical  science  have 
imposed  upon  mankind. 

witchcraft  was  unquestionable ;  '  for  first,  the  Scriptures  had  affirmed  so 
much ;  and  secondly,  the  wisdom  of  all  nations  had  provided  laws  against 
such  persons,  which  is  an  argument  of  their  confidence  of  such  a  crime.' 
Sir  Thomas  Browne,  who  was  a  great  physician  as  well  as  a  great  writer, 
was  called  as  a  witness,  and  swore  '  that  he  was  clearly  of  opinion  that 
the  persons  were  bewitched.'  "  —  Lecky's  History  of  Rationalism,  vol.  i. 
p.  120. 


MIRACLES  AND  SPECIAL  PROVIDENCES.  69 

Having  thus  submitted  Mr.  Mozley's  views  to  the  ex- 
amination which  they  challenged  at  the  hands  of  a  student 
of  the  order  of  Nature,  I  am  unwilling  to  quit  his  book 
without  expressing  my  high  admiration  and  respect  for  his 
ability.  His  failure,  as  I  consider  it  to  be,  must,  I  think, 
await  all  attempts,  however  able,  to  deal  with  the  material 
universe  by  logic  and  imagination,  unaided  by  experiment 
and  observation.  With  regard  to  the  style  of  the  book,  I 
willingly  subscribe  to  the  description  with  which  the  Times 
winds  up  its  able  and  appreciative  review.  "  It  is  marked 
throughout  with  the  most  serious  and  earnest  conviction, 
but  is  without  a  single  word  from  first  to  last  of  asperity  or 
insinuation  against  opponents,  and  this  not  from  any  de- 
ficiency of  feeling  as  to  the  importance  of  the  issue,  but 
from  a  deliberate  and  resolutely  maintained  self-control, 
and  from  an  overruling,  ever-present  sense  of  the  duty,  on 
themes  like  these,  of  a  more  than  judicial  calmness."  l 

[  To  the  argument  regarding  the  quantity  of  the  mirac- 
ulous, introduced  at  page  52,  Mr.  Mozley  has  done  me  the 
honor  of  publishing  a  reply  in  the  seventh  volume  of  the 
Contemporary  Jteview. — J.  T.,  1871.] 

1  See  Appendix  at  the  end  of  the  book. 


Library 

California 


IV. 
MATTER  AND  FORCE. 

A  LECTURE  TO  THE  WORKING-MEN  OF  DUNDEE. 

September  5,  1867. 


Heard  are  the  voices, 
Heard  are  the  sages, 
The  worlds  and  the  ages, 
*  Choose  well,  your  choice  is 
Brief  and  yet  endless. 

' '  Here  eyes  do  regard  you 
In  eternity's  stillness ; 
Here  is  all  fulness 
Ye  brave  to  reward  you, 
Work  and  despair  not.'  " 

GOETHE. 


IT. 

MATTER  AND  FORGE. 

IT  is  the  custom  of  the  Professors  in  the  Royal  School 
of  Mines  in  London  to  give  courses  of  evening  lectures 
every  year  to  working-men.  Each  course  is  duly  adver- 
tised, and  at  a  certain  hour  the  working-men  assemble  to 
purchase  tickets  for  the  course.  The  lecture-room  holds 
six  hundred  people,  and  tickets  to  this  amount  are  disposed 
of  as  quickly  as  they  can  be  handed  to  those  who  apply  for 
them.  So  desirous  are  the  working-men  of  London  to 
attend  these  lectures,  that  the  persons  who  fail  to  obtain 
tickets  always  bear  a  large  proportion  to  those  who  suc- 
ceed. Indeed,  if  the  lecture-room  could  hold  two  thousand 
instead  of  six  hundred,  I  do  not  doubt  that  every  one  of  its 
benches  would  be  occupied  on  these  occasions.  It  is, 
moreover,  worthy  of  remark  that  the  lectures  are  but  rarely 
of  a  character  which  could  help  the  working-man  in  his 
daily  pursuits.  The  knowledge  acquired  is  hardly  ever  of 
a  nature  which  admits  of  being  turned  into  money.  It  is  a 
pure  desire  for  knowledge,  as  a  thing  good  in  itself,  and 
without  regard  to  its  practical  application,  which  animates 
these  men.  They  wish  to  know  more  of  the  wonderful 
universe  around  them ;  their  minds  desire  this  knowledge 
as  naturally  as  their  bodies  desire  food  and  drink,  and  to 
satisfy  this  intellectual  want  they  come  to  the  School  of 
Mines. 

It  is  also  my  privilege  to  lecture  to  another  audience  in 
4 


74  FRAGMENTS  OF  SCIENCE. 

London,  composed  in  part  of  the  aristocracy  of  rank, 
while  the  audience  just  referred  to  is  composed  wholly  of 
the  aristocracy  of  labor.  As  regards  attention  and  cour- 
tesy to  the  lecturer,  neither  of  these  audiences  has  any 
thing  to  learn  of  the  other ;  neither  can  claim  superiority 
over  the  other.  I  do  not,  however,  think  that  it  would 
/  be  quite  correct  to  take  those  persons  who  flock  to  the 
School  of  Mines  as  average  samples  of  their  class ;  they 
are  probably  picked  men — the  aristocracy  of  labor,  as  I  have 
just  called  them.  At  all  events,  their  conduct  demonstrates 
that  the  essential  qualities  of  a  gentleman  are  confined 
to  no  class,  and  they  have  often  raised  in  my  mind  the 
wish  that  the  gentlemen  of  all  classes,  artisans  as  well  as 
lords,  could,  by  some  process  of  selection,  be  sifted  from 
the  general  mass  of  the  community,  and  caused  to  know 
each  other  better. 

When  pressed  some  months  ago  by  the  Council  of  the 
British  Association  to  give  an  evening  lecture  to  the  work- 
ing-men of  Dundee,  my  experience  of  the  working-men  of 
London  naturally  rose  to  my  mind ;  and,  though  heavily 
weighted  with  other  duties,  I  could  not  bring  myself  to  de- 
cline the  request  of  the  Council.  Hitherto,  the  evening 
discourses  of  the  Association  have  been  delivered  before 
its  members  and  associates  alone.  But  after  the  meeting 
at  Nottingham,  last  year,  where  the  working-men,  at  their 
own  request,  were  addressed  by  our  late  President,  Mr. 
Grove,  and  by  my  excellent  friend  Professor  Huxley,  the 
idea  rose  of  incorporating  with  all  subsequent  meetings  of 
the  Association  an  address  to  the  working-men  of  the  town 
in  which  the  meeting  is  held.  A  resolution  to  that  effect 
was  sent  to  the  Committee  of  Recommendations ;  the  com- 
mittee supported  the  resolution ;  the  Council  of  the  Asso- 
ciation ratified  the  decision  of  the  committee ;  and  here  I 
am  to  carry  out  to  the  best  of  my  ability  their  united 
wishes. 


MATTER  AND  FORCE.  75 

Whether  it  be  a  consequence  of  long-continued  develop- 
ment, or  an  endowment  conferred  once  for  all  on  man  at 
his  creation,  we  find  him  here  gifted  with  a  mind,  curious  'Is 
to  know  the  causes  of  things,  and  surrounded  by  objects 
which  excite  its  questionings,  and  raise  the  desire  for  an 
explanation.  It  is  related  of  a  young  prince  of  one  of  the 
Pacific  Islands,  that  when  he  first  saw  himself  in  a  looking- 
glass,  he  ran  round  the  glass  to  see  who  was  standing  at 
the  back.  And  thus  it  is  with  the  general  human  intellect, 
as  regards  the  phenomena  of  the  external  world.  It  wishes 
to  get  behind  and  learn  the  causes  and  connections  of  these  *• 
phenomena.  What  is  the  sun,  what  is  the  earth,  what 
should  we  see  if  we  came  to  the  edge  of  the  earth  and 
looked  over?  What  is  the  meaning  of  thunder  and  light- 
ning, of  hail,  rain,  storm,  and  snow  ?  Such  questions  pre- 
sented themselves  to  early  men,  and  by-and-by  it  was  dis- 
covered, that  this  desire  for  knowledge  was  not  implanted 
in  vain.  After  many  trials  it  became  evident  that  man's 
capacities  were,  so  to  speak,  the  complement  of  Nature's  - 
facts,  and  that,  within  certain  limits,  the  secret  of  the  uni- 
verse was  open  to  the  human  understanding.  It  was  found 
that  the  mind  of  man  had  the  power  of  penetrating  far  be- 
yond the  boundaries  of  his  five  senses ;  that  the  things 
which  are  seen  in  the  material  world  depend  for  their  action 
upon  things  unseen ;  in  short,  that  besides  the  phenomena 
which  address  the  senses,  there  are  laws  and  principles  and 
processes  which  do  not  address  the  senses  at  all,  but  which 
must  be,  and  can  be,  spiritually  discerned. 

There  are  two  things  which  form,  so  to  say,  the  sub- 
stance of  all  scientific  thought.  The  entire  play  of  the 
scientific  intellect  is  confined  to  the  combination  and  res- 
olution of  the  ideas  of  matter  and  force.  Newton,  it  is 
said,  saw  an  apple  fall.  To  the  common  mind  this  pre- 
sented no  difficulty  and  excited  no  question.  Not  so  with 
Newton.  He  observed  the  fact ;  but  one  side  of  his  great 


76  FRAGMENTS  OF  SCIENCE. 

intellectual  nature  was  left  unsatisfied  by  the  mere  act  of 
observation.  He  sought  after  the  principle  which  ruled 
the  fact.  Whether  this  anecdote  be  true  or  not,  it  illus- 
trates how  the  ordinary  operations  of  Nature,  which  most 
people  take  for  granted  as  perfectly  plain  and  simple,  are  ^ 
often  those  which  most  puzzle  the  scientific  man.  To  the 
conception  of  the  matter  of  the  apple,  Newton  added  that 
of  the  force  that  moved  it.  The  falling  of  the  apple  was 
due  to  an  attraction  exerted  mutually  between  it  and  the 
earth.  He  applied  the  idea  of  this  force  to  suns,  and  plan- 
ets, and  moons,  and  showed  that  all  their  motions  were 
necessary  consequences  of  this  attraction. 

Newton,  you  know,  was  preceded  by  a  grand  fellow 
named  John  Kepler — a  true  working-man — who,  by  analyz- 
ing the  astronomical  observations  of  his  master,  Tycho 
Brahe,  had  actually  found  that  the  planets  moved  as  they  are 
now  known  to  move.  As  a  matter  of  fact,  Kepler  knew  as 
much  about  the  motion  of  the  planets  as  Newton  did ;  in 
fact,  Kepler  taught  Newton  and  the  world  generally  the 
facts  of  planetary  motion.  But  this  was  not  enough.  The 
question  arose — Why  should  the  facts  be  so  ?  This  was 
the  great  question  for  Newton,  and  it  was  the  solution  of 
this  question  which  renders  his  name  and  fame  immortal. 
He  proved  that  the  planetary  motions  were  what  observa- 
tion made  them  to  be,  because  every  particle  of  matter  in 
the  solar  system  attracts  every  other  particle  by  a  force 
which  varies  as  the  inverse  square  of  the  distance  between 
the  particles.  He  showed  that  the  moon  fell  toward  the 
earth,  and  that  the  planets  fell  toward  the  sun,  through  the 
operation  of  the  same  force  that  pulls  an  apple  from  its 
tree.  This  all-pervading  force,  which  forms  the  solder  of 
the  material  universe,  and  the  conception  of  which  was 
necessary  to  Newton's  intellectual  peace,  is  called  the  force  " 
of  gravitation. 

All  force  may  be  ultimately  reduced  to  a  push  or  a  pull  in 


^  MATTER  AND   FORCE.  77 

a  straight  line  ;*but  its  manifestations  are  various,  and  some- 
times so  complex  as  entirely  to  disguise  its  elementary  con- 
stituents. Its  different  manifestations  have  received  differ- 
ent names.  Here,  for  example,  is  a  magnet  freely  suspended. 
I  bring  the  end  of  a  second  magnet  near  one  of  the  ends 
of  the  suspended  one — attraction  is  the  consequence.  I  re- 
verse the  position  of  one  of  the  magnets — repulsion  follows. 
This  display  of  power  is  called  magnetic  force.  In  the 
case  of  gravitation  we  have  a  simple  attraction,  in  the  case 
of  magnetism  attraction  and  repulsion  always  go  together. 
Thus  magnetism  is  a  double  force,  or,  as  it  is  usually  called, 
a  polar  force.  I  present  a  bit  of  common  iron  to  the  magnet, 
the  iron  itself  becomes  a  temporary  magnet,  and  it  now 
possesses  the  power  of  attracting  other  iron.  And  if  sev- 
eral pieces  of  iron  be  presented  at  the  same  time,  not  only 
will  the  magnet  act  on  them,  but  they  will  also  act  upon 
each  other. 

This  leads  me  to  j&if  experiment  which  will  give  you 
some  idea  of  how  bodies  arrange  themselves  under  the 
operation  of  a  polar  force.  Underneath  this  plate  of  glass 
is  placed  a  small  magnet,  and  by  an  optical  arrangement 
comprising  a  powerful  lamp,  a  magnified  image  of  the  mag- 
net is  now  cast  upon  the  screen  before  you.  I  scatter  iron 
filings  over  the  glass.  You  already  notice  a  certain  arrange- 
ment of  the  particles  of  iron.  Their  free  action  is,  how- 
ever, hampered  by  friction.  I  therefore  tap  the  glass, 
liberate  the  particles,  which,  as  I  tap,  arrange  themselves  in 
these  beautiful  curves.  This  experiment  is  intended  to 
make  clear  to  you  how  a  definite  arrangement  of  particles 
— a  kind  of  incipient  structure — may  result  from,  the  oper- 
ation of  a  polar  force.  We  shall  by-and-by  see  far  more 
wonderful  exhibitions  of  the  same  structural  action  when 
we  come  to  deal  with  the  force  of  crystallization. 

The  magnetic  force  has  here  acted  upon  particles  of 
matter  visible  to  the  eye.  But,  as  already  stated,  there  are 


78  FKAGMENTS  OF  SCIENCE. 

numerous  processes  in  Nature  which  entirely  elude  the  eye 
of  the  body,  and  must  be  figured  by  the  eye  of  the  mind. 
The  processes  of  chemistry  are  examples  of  these.  Long 
thinking  and  experimenting  on  the  materials  which  compose 
our  world  have  led  philosophers  to  conclude  that  matter  is 
composed  of  atoms  from  which,  whether  separate  or  in  com- 
bination, the  whole  material  world  is  built  up.  The  air  we 
breathe,  for  example,  is  mainly  a  mixture  of  the  atoms  of 
two  distinct  substances,  called  oxygen  and  nitrogen.  The 
water  we  drink  is  also  composed  of  two  distinct  substances, 
called  oxygen  and  hydrogen.  But  it  differs  from  the  air  in 
this  particular,  that  in  water  the  oxygen  and  hydrogen  are 
not  mechanically  mixed,  but  chemically  combined.  In  fact, 
the  atoms  of  oxygen  and  those  of  hydrogen  exert  enormous 
attractions  on  each  other,  so  that  when  brought  into  sufficient 
proximity  they  rush  together  with  an  almost  incredible 
force  to  form  a  chemical  compound.  But  powerful  as  is  the 
force  with  which  these  atoms  lock  themselves  together,  we 
have  the  means  of  tearing  them  asunder,  and  the  agent  by 
which  we  accomplish  this  may  here  receive  a  few  moments' 
attention. 

Into  a  vessel  containing  acidulated  water  I  dip  these 
two  strips  of  metal,  the  one  being  zinc  and  the  other  plati- 
num, not  permitting  them  to  touch  each  other  in  the  liquid. 
I  now  connect  the  two  upper  ends  of  the  strips  by  a  piece 
of  copper  wire.  The  wire  is  apparently  unchanged,  but  it 
is  not  so  in  reality.  It  is  now  the  channel  of  what,  for 
want  of  a  better  name,  we  call  an  electric  current — a  power 
generated  and  maintained  by  the  chemical  action  going  on 
in  the  vessel  of  acidulated  water.  What  the  inner  change 
of  the  wire  is  we  do  not  know,  but  we  do  know  that  a  change 
has  occurred,  by  the  external  effects  produced  by  the  wire. 
Let  me  show  you  one  or  two  of  these  effects.  And  here  it 
is  convenient  to  operate  with  greater  power  than  can  be  ob- 
tained from  a  single  small  pair  of  strips  of  metal,  and  a 


MATTER  AND  FORCE.  79 

single  vessel  of  acidulated  water.  Before  you  is  a  series  of 
ten  vessels,  each  with  its  pair  of  metals,  and  I  wish  to  get 
the  added  force  of  all  ten.  This  arrangement  is  called  a 
voltaic  battery.  I  take  a  piece  of  copper  wire  in  my  hand, 
and  plunge  it  among  these  iron  filings ;  they  refuse  to  cling 
to  it ;  the  wire  has  no  power  over  the  filings.  J  now  em- 
ploy the  self-same  wire  to  connect  the  two  ends  of  the  bat- 
tery, and  subject  it  to  the  same  test.  The  iron  filings  now 
crowd  round  the  wire  and  cling  to  it.  This  is  one  of  the 
effects  of  the  electric  current  now  traversing  the  wire.  I 
interrupt  the  current,  and  the  filings  immediately  fall ;  the 
power  of  attraction  continues  only  so  long  as  the  wire  con- 
nects the  two  ends  of  the  battery. 

Here  is  a  piece  of  similar  wire,  overspun  with  cotton,  to 
prevent  the  contact  of  its  various  parts.  It  is  formed  into 
a  coil,  which  at  present  has  no  power  over  these  iron  nails  ; 
but  I  now  make  the  coil  part  of  the  wire  which  connects 
the  two  ends  of  the  voltaic  battery.  No  visible  change  has 
occurred  in  the  coil,  but  it  is  no  longer  what  it  was.  By 
the  attractive  force  with  which  it  has  become  suddenly  en- 
dowed, it  now  empties  this  tool-box  of  its  nails.  I  twist  a 
covered  copper  wire  round  this  common  poker.  At  present 
the  poker  is  powerless  over  these  iron  nails  ;  but  when  we 
connect  with  the  wire  surrounding  the  poker  the  two  ends 
of  the  voltaic  battery,  the  poker  is  instantly  transformed 
into  a  strong  magnet.  Here,  again,  are  two  flat  spirals  sus- 
pended facing  each  other.  They  are  about  six  inches 
apart.  By  turning  this  handle  in  a  certain  direction  a  cur- 
rent is  sent  through  both  spirals.  When  this  is  done  they 
clash  suddenly  together,  being  drawn  together  by  their  mu- 
tual attraction.  By  turning  the  handle  in  another  direction, 
I  reverse  what  is  called  the  direction  of  the  current  in  one 
of  the  spirals,  and  now  they  fly  asunder,  being  driven  apart 
by  their  mutual  repulsion.  All  these  effects  are  due  to  the 
power  which  we  name  an  electric  current,  and  which  we 


80  FRAGMENTS  OF  SCIENCE. 

figure  as  flowing  through  the  wire  when  the  voltaic  circuit 
is  complete. 

I  have  said  that  no  visible  change  occurs  in  the  wire 
when  the  current  passes  through  it.  Still  a  change  over 
and  above  what  you  have  seen  really  does  take  place.  Lay 
hold  of  those  spirals,  and  you  will  find  them  warm.  Let 
me  exalt  this  warmth  so  as  to  render  it  visible  to  you.  In 
front  of  the  table  is  a  thin  platinum  wire  six  feet  long.  On 
sending  a  current  from  a  battery  of  fifty  pairs  of  plates 
through  this  wire  it  glows,  as  you  see,  vividly  red.  I  shorten 
the  wire ;  more  electricity  now  flows  through  it,  and  its 
light  becomes  more  intense.  It  is  now  bright  yellow ;  and 
now  it  is  a  dazzling  white.  This  light  is  so  strong  that 
though  the  wire  is  not  much  thicker  than  a  bristle,  it  ap- 
pears to  those  on  the  nearest  benches  as  thick  as  a  quill ; 
while  to  those  at  a  distance  it  appears  as  thick  as  a  man's 
finger.  This  effect,  which  we  call  irradiation,  is  always  pro- 
duced by  a  very  strong  light.  It  is  this  same  electric  cur- 
rent that  furnished  us  with  the  powerful  light  employed  in 
one  of  our  first  experiments.  The  lamp  then  made  use  of 
is  provided  with  these  coke  rods ;  and  when  the  electric 
current  passes  between  them  we  obtain  a  light  almost  as 
brilliant  as  that  of  the  sun. 

And  now  let  us  return  to  the  point  at  which  the  elec- 
tric current  was  introduced— the  point,  namely,  where  the  t 
tearing  asunder  of  the  locked  atoms  of  a  chemical  com- 
pound was  spoken  of.  The  agent  by  which  we  effect  this 
is  also  the  electric  current;  and  I  hope  to  make  its  action 
visible  to  you  all.  Into  this  small  cell,  containing  water, 
dip  two  thin  wires.  By  means  of  a  solar  microscope  and 
the  powerful  light  of  our  electric  lamp,  a  magnified  image 
of  this  cell  is  thrown  upon  the  screen  before  you.  You 
see  plainly  the  images  of  the  wires.  And  now  I  send 
from  a  second  small  battery  which  rests  upon  this  table  an 
electric  current  from  wire  to  wire.  Bubbles  of  gas  rise 


MATTER  AND  FORCE.  81 

immediately  from  each  of  them,  and  these  are  the  two 
gases  of  which  the  water  is  composed.  The  oxygen  is 
always  liberated  on  the  one  wire,  the  h}*drogen  on  the 
other.  The  two  gases  may  be  collected  separately ;  in 
fact,  they  have  been  thus  collected  in  these  jars.  A  lighted 
taper'placed  in  one  jar  inflames  the  gas,  which  proves  it  to 
be  hydrogen ;  a  burning  ember  of  wood  placed  in  the 
other  jar  instantly  bursts  into  vivid  combustion,  which 
proves  the  gas  in  the  jar  to  be  oxygen.  I  place  upon  my 
hand  a  soap-bubble  filled  with  a  mixture  of  both  gases  in 
the  exact  proportions  in  which  they  exist  in  water.  Apply- 
ing a  taper  to  the  bubble,  a  loud  explosion  is  heard.  The 
gases  have  rushed  together  with  detonation,  but  without 
injury  to  my  hand,  and  the  water  from  which  they  were 
extracted  is  the  result  of  the  reunion. 

I  wish  you  to  see  with  the  utmost  possible  clearness  " 
what  has  here  taken  place^  First,  then,  you  are  to  re- 
member that  to  form  water  the  proportions  by  weight  of 
oxygen  and  hydrogen  are  as  eight  to  one.  Eight  ounces 
of  oxygen,  for  example,  unite  with  one  of  hydrogen  to 
form  nine  ounces  of  water.  But  if,  instead  of  comparing 
weights,  we  compare  volumes,  two  volumes  of  hydrogen 
unite  with  one  of  oxygen  to  form  water.  Now,  these  vol- 
umes, and  not  the  weights,  express  the  proportions  in 
which  the  atoms  of  hydrogen  unite  with  those  of  oxygen. 
In  the  act  of  combination  two  atoms  of  hydrogen  combine 
with  one  of  oxygen  to  form  what  we  call  the  molecule  of 
water.  Every  such  molecule  is  a  group  of  three  atoms, 
two  of  which  are  hydrogen  and  one  oxygen. 

One  consequence  of  the  rushing  together  of  the  atoms 
is  the  development  of  heat.  What  is  this  heat  ?  How 
are  we  to  figure  it  before  our  minds  ?  I  do  not  despair  of 
being  able  to  give  you  a  tolerably  distinct  answer  to  this 
question.  Here  are  two  ivory  balls  suspended  from  the 
same  point  of  support  by  two  short  strings.  I  draw  them 


82  FRAGMENTS  OF  SCIENCE. 

thus  apart  and  then  liberate  them.  They  clash  together, 
but,  by  virtue  of  their  elasticity,  they  quickly  recoil  from 
each  other,  and  a  sharp  vibratory  rattle  succeeds  their  col- 
lision. This  experiment  will  enable  you  to  figure  to  your 
mind  a  pair  of  clashing  atoms.  We  have,  in  the  first  place, 
a  motion  of  the  one  atom  toward  the  other — a  motion  of 
translation,  as  it  is  usually  called.  But  when  the  atoms 
come  sufficiently  near  each  other,  elastic  repulsion  sets  in, 
the  motion  of  translation  is  stopped  and  converted  into  a 
motion  of  vibration.  To  this  vibratory  motion  we  give  the 
name  of  heat.  Thus,  three  things  are  to  be  kept  before 
the  mind — first,  the  atoms  themselves  ;  secondly,  the  force 
Avith  which  they  attract  each  other;  and  thirdly,  the  mo- 
tion consequent  upon  the  exertion  of  that  force.  This  mo- 
tion must  be  figured  first  as  a  motion  of  translation,  and 
then  as  a  motion  of  vibration  ;  and  it  is  not  until  the  mo- 
tion reaches  the  vibratory  stage  that  we  give  it  the  name 
of  heat.  It  is  this  motion  imparted  to  the  nerves  that  pro- 
duces the  sensation  of  heat. 

It  would  be  useless  to  attempt  a  more  detailed  'descrip- 
tion of  this  molecular  motion.  After  the  atoms  have 
been  thrown  into  this  state  of  agitation,  very  complicated 
motions  must  ensue  from  their  incessant  collision.  There 
must  be  a  wild  whirling  about  among  the  molecules.  For 
some  time  after  the  act  of  combination  this  action  is  so 
violent  as  to  prevent  the  molecules  from  coming  together. 
The  water  is  maintained  for  a  time  in  a  state  of  vapor. 
But  as  the  vapor  cools,  or  in  other  words  loses  its  mo- 
tion, the  water  molecules  coalesce  to  form  a  liquid.  And 
now  we  are  approaching  a  new  and  wonderful  display  of 
force.  No  one  who  had  only  seen  water  in  its  vaporous  or 
liquid  form  could  imagine  the  existence  of  the  forces  now 
to  be  referred  to  ;  for  as  long  as  the  substance  remains  in 
a  liquid  or  vaporous  condition,  the  play  of  these  forces  is 
altogether  masked  and  hidden.  But  let  the  heat  be  gradu- 


MATTER  AND  FORCE.  83 

ally  withdrawn,  the  antagonist  to  their  union  being  re- 
moved, the  molecules  prepare  for  new  arrangements  and 
combinations.  Like  the  particles  of  iron  in  our  magnetic 
experiment,  the  water  molecules  are  endowed  with  attractive 
and  repulsive  poles,  and  they  arrange  themselves  together 
in  accordance  with  these  attractions  and  repulsions.  Solid 
crystals  of  water  are  thus  formed,  to  which  we  give  the  fa- 
miliar name  of  ice.  To  the  eye  of  science  these  ice-crystals 
are  as  precious  as  the  diamond — as  purely  formed,  as  deli- 
cately built.  Where  no  disturbing  causes  intervene,  there 
is  no  disorder  in  this  crystalline  architecture.  By  their  own 
constructive  power  molecule  builds  itself  on  to  molecule 
with  a  precision  far  greater  than  that  attainable  by  the 
hands  of  man.  We  are  apt  to  overlook  the  wonderful  when 
it  becomes  common.  Imagine  the  bricks  and  stones  of 
this  town  of  Dundee  endowed  with  locomotive  power.  Im- 
agine them  attracting  and  repelling  each  other,  and  arrang- 
ing themselves  in  consequence  of  these  attractions  and  re- 
pulsions to  form  streets  and  houses  and  Kinnaird  Halls ; 
would  not  that  be  wonderful  ?  Hardly  less  wonderful  is 
the  play  of  force  by  which  the  molecules  of  water  build 
themselves  into  the  sheets  of  crystal  which  every  winter 
roof  your  ponds  and  lakes. 

If  I  could  show  you  the  actual  progress  of  this  molecu- 
lar architecture,  its  beauty  would  delight  and  astonish  you. 
A  reversal  of  the  process  may  be  actually  shown.  The 
molecules  of  a  piece  of  ice  may  be  taken  asunder  before 
your  eyes,  and  from  the  manner  in  which  they  separate,  you 
may  to  some  extent  infer  the  manner  in  which  they  aggre- 
gate. When  a  beam  is  sent  from  our  electric  lamp  through 
a  plate  of  glass,  a  portion  of  the  beam  is  intercepted,  and 
the  glass  is  warmed  by  the  portion  thus  retained  within  it. 
When  the  beam  is  sent  through  a  plate  of  ice,  a  portion 
of  the  beam  is  also  absorbed ;  but  instead  of  warming  the 
ice,  the  intercepted  heat  melts  it  internally.  It  is  to  the 


84  FRAGMENTS  OF  SCIENCE. 

delicate,  silent  action  of  this  beam  within  the  ice  that  I 
now  wish  to  direct  your  attention.  Upon  the  screen  is 
thrown  a  magnified  image  of  the  slab  of  ice :  the  light  of 
the  beam  passes  freely  through  the  ice  without  melting  it, 
and  enables  us  to  form  the  image,  but  the  heat  of  the 
beam  is  in  great  part  intercepted  by  the  ice,  and  that  heat 
now  applies  itself  to  the  work  of  internal  liquefaction. 
Observe  those  stars  breaking  out  over  the  white  surface, 
and  expanding  in  size  as  the  action  of  the  beam  continues. 
These  stars  are  liquefied  ice,  and  each  of  them,  you  ob- 
serve, has  six  rays.  They  still  more  closely  resemble 
flowers,  each  of  six  petals.  Under  the  action  of  the  heat 
the  molecules  of  the  ice  fall  asunder,  so  as  to  leave  be- 
hind them  these  exquisite  forms.  We  have  here  the  pro- 
cess of  crystallization  reversed.  In  this  fashion,  and  in 
strict  accordance  with  this  hexangular  type  every  ice  mole- 
cule takes  its  place  upon  our  ponds  and  lakes  during  the 
frosts  of  winter.  To  use  the  language  of  an  American 
poet,  "  the  atoms  march  in  tune,"  moving  to  the  music  of 
law,  which  thus  renders  the  commonest  substance  in  Na- 
ture a  miracle  of  beauty. 

It  is  the  function  of  science,  not  as  some  think  to  divest^ 
this  universe  of  its  wonder  and  its  mystery,  but,  as  in  the 
case  here  before  us,  to  point  out  the  wonder  and  the 
mystery  of  common  things.  Those  fern-like  forms,  which 
on  a  frosty  morning  overspread  your  window-panes,  illus- 
trate the  action  of  the  same  force.  Breathe  upon  such  a 
pane  before  the  fires  are  lighted,  and  reduce  the  solid  crys- 
talline film  to  the  liquid  condition,  then  watch  its  subse- 
quent appearance.  You  will  see  it  all  the  better  if  you 
look  at  it  through  a  common  magnifying-glass.  After  you 
have  ceased  breathing,  the  film,  abandoned  to  the  action  of 
its  own  forces,  appears  for  a  moment  to  be  alive.  Lines  of 
motion  run  through  it ;  molecule  closes  with  molecule,  until 
finally  the  whole  film  passes  from  the  state  of  liquidity, 


MATTER  AND  FORCE.  85 

through   this  state  of  motion,  to  its  final  crystalline  re- 
pose. 

[  ft  I  can  show  you  something  similar.  Over  a  piece  of 
perfectly  clean  glass  I  pour  a  little  water  in  which  a  crystal 
has  been  dissolved.  A  film  of  the  solution  clings  to  the 
glass,  and  this  film  will  now  be  caused  to  crystallize  before 
your  eyes.  By  means  of  a  microscope  and  a  lamp,  an  image 
of  the  plate  of  glass  is  thrown  upon  the  screen.  The  beam 
of  the  lamp,  besides  illuminating  the  glass,  also  heats  it ; 
evaporation  sets  in,  and,  at  a  certain  moment,  when  the 
solution  has  become  supersaturated,  splendid  branches  of 
crystals  shoot  out  over  the  screen.  A  dozen  square  feet  of 
surface  are  now  covered  by  those  beautiful  forms.  With 
another  solution  we  obtain  crystalline  spears,  feathered 
right  and  left  by  other  spears.  From  distant  nuclei  in 
the  middle  of  the  field  of  view  the  spears  shoot  with  magical 
rapidity  in  all  directions.  The  film  of  water  on  a  window- 
pane  on  a  frosty  morning  exhibits  effects  quite  as  wonderful 
as  these.  Latent  in  this  formless  solution,  latent  in  every 
drop  of  water,  lies  this  marvellous  structural  power,  which 
only  requires  the  withdrawal  of  opposing  forces  to  bring  it 
into  action. 

Our  next  experiment  on  crystallization  you  will  probably 
consider  more  startling  even  than  these.  The  clear  liquid 
now  held  up  before  you  is  a  solution  of  nitrate  of  silver — a 
compound  of  silver  and  nitric  acid.  When  an  electric  cur- 
rent is  sent  through  this  liquid  the  silver  is  severed  from 
the  acid,  as  the  hydrogen  was  separated  from  the  oxygen 
in  a  former  experiment ;  and  I  would  ask  you  to  observe 
how  the  metal  behaves  when  its  molecules  are  thus  succes- 
sively set  free.  The  image  of  the  cell,  and  of  the  two  wires 
which  dip  into  the  liquid  of  the  cell,  are  now  clearly  shown 
upon  the  screen.  Let  us  close  the  circuit,  and  send  the 
current  through  the  liquid.  From  one  of  the  wires  a  beau- 
tiful silver  tree  commences  immediately  to  sprout.  Branches 


86  FRAGMENTS  OF  SCIENCE. 

of  the  metal  are  thrown  out,  and  umbrageous  foliage  loads 
the  branches.  You  have  here  a  growth  apparently  as  won- 
derful as  that  of  any  vegetable  perfected  in  a  minute  before 
your  eyes.  Substituting  for  the  nitrate  of  silver  acetate  of 
lead,  which  is  a  compound  of  lead  and  acetic  acid,  the 
electric  current  severs  the  lead  from  the  acid,  and  there  you 
see  the  metal  slowly  branching  into  these  exquisite  metallic 
ferns,  the  fronds  of  which,  as  they  become  too  heavy,  break 
from  their  roots  and  fall  to  the  bottom  of  the  cell. 

These  experiments  show  that  the  common  matter  of  our 
earth — "  brute  matter,"  as  Dr.  Young  pleases  to  call  it — 
when  its  atoms  and  molecules  are  permitted  to  bring  their 
forces  into  free  play,  arranges  itself,  under  the  operation  of 
these  forces,  into  forms  which  rival  in  beauty  those  of  the 
vegetable  world.  And  what  is  the  vegetable  world  itself 
but  the  result  of  the  complex  play  of  these  molecular  forces  ? 
Here,  as  elsewhere  throughout  Nature,  if  matter  moves,  it 
is  force  that  moves  it ;  and  if  a  certain  structure,  vegetable 
or  mineral,  is  produced,  it  is  through  the  operation  of  the 
forces  exerted  between  the  atoms  and  molecules.  These 
atoms  and  molecules  resemble  little  magnets  with  mutually 
attractive  and  mutually  repellant  poles.  The  attracting 
poles  unite,  the  repellant  poles  retreat,  and  vegetable  as 
well  as  mineral  forms  are  the  final  expression  of  this  com- 
plicated molecular  action. 

In  the  formation  of  our  lead  and  silver  trees,  we  needed 
an  agent  to  wrest  the  lead  and  the  silver  from  the  acids 
with  which  they  were  combined.  A  similar  agent  is  re- 
quired in  the  vegetable  world.  The  solid  matter  of  which 
our  lead  and  silver  trees  were  formed  was,  in  the  first  in- 
stance, disguised  in  a  transparent  liquid ;  the  solid  matter 
of  which  our  woods  and  forests  are  composed  is  also,  for 
the  most  part,  disguised  in  a  transparent  gas,  which  is 
mixed  in  small  quantities  with  the  air  of  our  atmosphere. 
This  gas  is  formed  by  the  union  of  carbon  and  oxygen,  and 


MATTER  AND  FORCE.  87 

is  called  carbonic  acid  gas.  Two  atoms  of  oxygen  and  one 
of  carbon  unite  to  fonn  the  molecule  of  carbonic  acid  which, 
as  I  have  said,  is  the  material  from  which  wood  and  vege- 
table tissues  are  mainly  derived.  The  carbonic  acid  of  the 
air  being  subjected  to  an  action  somewhat  analogous  to 
that  of  the  electric  current  in  the  case  of  our  lead  and  silver 
solutions,  has  its  carbon  liberated  and  deposited  as  woody 
fibre.  The  watery  vapor  of  the  air  is  subjected  to  similar 
action ;  its  hydrogen  is  liberated  from  its  oxygen,  and  lies 
down  side  by  side  with  the  carbon  in  the  tissues  of  the 
tree.  The  oxygen  in  both  cases  is  permitted  to  wander 
away  into  the  atmosphere.  But  what  is  it  which  thus  tears 
the  carbon  and  the  hydrogen  from  the  strong  embrace  of 
the  oxygen  ?  What  is  it  in  Nature  that  plays  the  part  of 
the  electric  current  in  our  experiments  ?  The  rays  of  the,//' 
sun.  The  leaves  of  the  plants  absorb  both  the  carbonic 
acid  and  the  aqueous  vapor  of  the  air;  these  leaves  an- 
swer to  the  cells  in  which  our  decompositions  by  the  electric 
current  took  place.  In  the  leaves  the  solar  rays  decompose 
both  the  carbonic  acid  and  the  water,  permitting  the  oxygen 
in  both  cases  to  escape  into  the  air,  and  allowing  the  carbon 
and  the  hydrogen  to  follow  the  bent  of  their  own  forces. 
And  just  as  the  molecular  attractions  of  the  silver  and  the 
lead  found  expression  in  the  production  of  those  beautiful 
branching  forms  seen  in  our  experiments,  so  do  the  molecular 
attractions  of  the  liberated  carbon  and  hydrogen  find  ex- 
pression in  the  architecture  of  grasses,  plants,  and  trees. 

In  the  fall  of  a  cataract  and  the  rush  of  the  wind  we 
have  examples  of  mechanical  power.  In  the  combinations 
of  chemistry  and  in  the  formation  of  crystals  and  vegetables 
we  have  examples  of  molecular  power.  But  before  pro- 
ceeding further  I  should  like  to  make  clear  to  you  the 
present  condition  of  the  surface  of  our  globe  with  reference 
to  power  generally.  You  have  learned  how  the  atoms  of 
oxygen  and  hydrogen  rush  together  to  form  water.  I  have 


88  FRAGMENTS  OF  SCIENCE. 

not  thought  it  necessary  to  dwell  upon  the  mighty  mechani- 
cal energy  of  their  act  of  combination,  but,  in  passing,  I 
would  say  that  the  clashing  together  of  1  Ib.  of  hydrogen 
and  8  Ibs.  of  oxygen  to  form  9  Ibs.  of  aqueous  vapor,  is 
greater  than  the  clash  of  a  weight  of  1,000  tons  falling 
from  a  height  of  20  feet  against  the  earth.  Now,  in  order 
that  the  atoms  of  oxygen  arid  hydrogen  should  rise  by  their 
mutual  attractions  to  the  velocity  corresponding  to  this 
enormous  mechanical  effect,  a  certain  distance  must  exist 
between  the  particles.  It  is  in  rushing  over  this  that  the 
velocity  is  attained. 

This  idea  of  distance  between  the  attracting  atoms  is  of 
the  highest  importance  in  our  conception  of  the  system,  of 
the  world.  For  the  world  may  be  divided  into  two  kinds 
of  matter ;  or  rather  the  matter  of  the  world  may  be  classi- 
fied under  two  distinct  heads — namely,  of  atoms  and  mole- 
cules which  have  already  rushed  together  and  thus  satisfied 
their  mutual  attractions,  and  of  atoms  and  molecules  which 
have  not  yet  rushed  together,  and  whose  mutual  attractions 
are,  therefore,  as  yet  unsatisfied.  Now,  as  regards  motive 
power,  the  working  of  machinery,  or  the  performance  of 
mechanical  work  generally,  by  means  of  the  materials  of 
the  earth's  crust,  we  are  entirely  dependent  on  those  atoms/' 
and  molecules  whose  attractions  are  as  yet  unsatisfied.  Those 
attractions  can  produce  motion,  because  sufficient  distance 
intervenes  between  the  attracting  molecules,  and  it  is  this 
molecular  motion  that  we  utilize  in  our  machines.  Thus 
we  can  get  power  out  of  oxygen  and  hydrogen  by  the  act 
of  their  union,  but  once  they  are  combined,  and  once  the 
motion  consequent  on  their  combination  has  been  expended, 
no  further  power  can  be  got  out  of  the  mutual  attraction 
of  oxygen  and  hydrogen.  As  dynamic  agents  they  are 
dead.  If  we  examine  the  materials  of  which  the  earth's 
crust  is  composed,  we  find  them  to  consist  for  the  most  part 
of  substances  whose  atoms  have  already  closed  in  chemical 


MATTER  AND  FORCE.  89 

union — whose  mutual  attractions  are  satisfied.  Granite, 
for  instance,  is  a  widely-diffused  substance,  but  granite 
consists,  in  great  part,  of  silicon,  oxygen,  potassium,  cal- 
cium, and  aluminum,  the  atoms  of  which  substances  met 
long  ago  in  chemical  combination,  and  are  therefore  dead. 
Limestone  is  also  a  widely-diffused  substance.  It  is  com- 
posed of  carbon,  oxygen,  and  a  metal  called  calcium.  But 
the  atoms  of  those  substances  closed  long  ago  in  chemical 
union,  and  are  therefore  dead.  And  in  this  way  we  might 
go  over  the  whole  of  the  materials  of  the  earth's  crust,  and 
satisfy  ourselves  that  though  they  were  sources  of  power  in 
ages  past,  and  long  before  any  being  appeared  on  the 
surface  of  the  earth  capable  of  turning  their  power  to 
account,  they  are  sources  of  power  no  longer.  And  here 
we  might  halt  for  a  moment  to  remark  on  that  tendency, 
so  prevalent  in  the  world,  to  regard  every  thing  as  made  for 
human  use.  Those  who  entertain  this  notion  hold,  I  think, 
an  overweening  opinion  of  their  own  importance  in  the 
system  of  Nature.  Flowers  bloomed  before  men  saw  them, 
and  the  quantity  of  power  wasted  before  man  could  utilize 
it  is  all  but  infinite  compared  with  what  now  remains  to  be 
applied.  The  healthy  attitude  of  mind  with  reference  to 
this  subject  is  that  of  the  poet,  who,  when  asked  whence 
came  the  rhodora,  replied : 

"  Why  thou  wert  there,  0  rival  of  the  rose  ! 

I  never  thought  to  ask,  I  never  knew, 
But  in  my  simple  ignorance  supposed 

The  self-same  power  that  brought  me  there  brought  you."  1 

A  few  exceptions  to  this  general  state  of  union  of  the 
particles  of  the  earth's  crust — all-important  to  us,  but  trivial 
in  comparison  to  the  total  store  of  which  they  are  the  resi- 
due— still  remain.  They  constitute  our  main  sources  of 
motive  power.  By  far  the  most  important  of  these  are  our 
1  Emerson. 


90  FRAGMENTS  OF  SCIENCE. 

beds  of  coal,  composed  chiefly  of  carbon,  which  has  not  yet 
closed  in  chemical  union  with  oxygen.  Distance  still  inter- 
venes between  the  atoms  of  carbon  and  those  of  oxygen, 
across  which  the  atoms  may  be  impelled  by  their  mutual 
attractions,  and  we  can  do  nothing  more  than  utilize  the 
motion  produced  by  this  attraction.  Once  the  carbon  and 
the  oxygen  have  rushed  together,  so  as  to  form  carbonic 
acid,  their  mutual  attractions  are  satisfied,  and,  while  they 
continue  in  this  condition,  as  dynamic  agents  they  are  dead. 
A  pound  of  coal  produces  by  its  combination  with  oxygen 
an  amount  of  heat  which,  if  mechanically  applied,  would 
raise  a  weight  of  100  Ibs.  to  a  height  of  twenty  miles  above 
the  earth's  surface.  Conversely,  100  Ibs.  falling  from  a 
height  of  twenty  miles,  and  striking  against  the  earth, 
would  generate  an  amount  of  heat  equal  to  that  devel- 
oped by  the  combustion  of  a  pound  of  coal.  Wherever 
work  is  done  by  heat,  heat  disappears.  A  gun  which  fires 
a  ball  is  less  heated  than  one  which  fires  blank  cartridge. 
The  quantity  of  heat  communicated  to  the  boiler  of  a 
working  steam-engine  is  greater  than  that  which  could  be 
obtained  from  the  recondensation  of  the  steam  after  it  had 
done  its  work ;  and  the  amount  of  work  performed  is  the 
exact  equivalent  of  the  amount  of  heat  missing.  We  dig 
annually  nearly  100  millions  of  tons  of  coal  from  our  pits. 
The  amount  of  mechanical  force  represented  by  this  quantity 
of  coal  seems  perfectly  fabulous.  The  combustion  of  a 
single  pound  of  coal,  supposing  it  to  take  place  in  a  minute, 
would  be  equivalent  to  the  work  of  300  horses;  and  if  we 
suppose  120  millions  of  horses  working  day  and  night  with 
unimpaired  strength,  for  a  year,  their  united  energies  would 
enable  them  to  perform  an  amount  of  work  just  equivalent 
to  the  heat  to  be  derived  from  the  annual  produce  of  our 
coal-fields.  Our  woods  and  forests  are  also  sources  of 
mechanical  energy,  because  they  also  have  the  power  of 
uniting  with  the  atmospheric  oxygen,  and  the  molecular 


MATTER  AND  FORCE.  91 

motion  produced  in  the  act  of  union  may  be  turned  to 
mechanical  account.  Passing  from  dead  matter  to  living  ^ 
matter,  we  find  that  the  source  of  motive  power  here  re- 
ferred to  is  also  the  source  of  muscular  power.  A  horse 
can  perform  work,  and  so  can  a  man,  but  this  work  is  at 
bottom  the  molecular  work  of  the  elements  of  the  food  and 
the  oxygen  of  the  air.  We  inhale  this  vital  gas,  and  bring 
it  into  sufficiently  close  proximity  with  the  carbon  and  the 
hydrogen  of  the  food.  They  unite  in  obedience  to  their 
mutual  attractions,  and  their  motion  toward  each  other, 
properly  turned  to  account  by  the  wonderful  mechanism  of 
the  body,  becomes  muscular  motion. 

One  fundamental  thought  pervades  all  these  statements :  / 
there  is  one-tap  root  from  which  they  all  spring.  This  is 
the  ancient  maxim  that  out  of  nothing  nothing  comes  ;  that 
neither  in  the  organic  world  nor  in  the  inorganic  is  power 
produced  without  the  expenditure  of  other  power;  that 
neither  in  the  plant  nor  in  the  animal  is  there  a  creation  of 
force  or  motion.  Trees  grow,  and  so  do  men  and  horses  ;^ 
and  here  we  have  new  power  incessantly  introduced  upon 
the  earth.  But  its  source,  as  I  have  already  stated,  is  the 
sun.  For  he  it  is  who  separates  the  carbon  from  the  oxy- 
gen of  the  carbonic  acid,  and  thus  enables  them  to  recom- 
bine.  Whether  they  recombine  in  the  furnace  of  the 
steam-engine  or  in  the  animal  body,  the  origin  of  the  power 
they  produce  is  the  same.  In  this  sense  we  are  all  "  souls 
of  fire  and  children  of  the  sun."  But,  as  remarked  by 
Helmholtz,  we  must  be  content  to  share  our  celestial 
pedigree  with  the  meanest  living  things.  The  frog,  and 
the  toad,  and  those  terrible  creatures,  the  monkey  and  {/ 
the  gorilla,  draw  their  power  from  the  same  source  as 
man. . 

Some  estimable  persons,  here  present,  very  possibly 
shrink  from  accepting  these  statements ;  they  may  be 
frightened  by  their  apparent  tendency  toward  what  is  called 


92  FRAGMENTS  OF  SCIENCE. 

materialism — a  word  which,  to  many  minds,  expresses  some- 
thing very  dreadful.  But  it  ought  to  be  known  and  avowed 
that  the  physical  philosopher,  as  such,  must  be  a  pure  ma- 
terialist. His  inquiries  deal  with  matter  and  force,  and 
with  them  alone.  The  action  which  he  has  to  investigate 
is  necessary  action ;  not  spontaneous  action — the  transfor- 
mation, not  the  creation,  of  matter  and  force.  And  what- 
ever be  the  forms  which  matter  and  force  may  assume, 
whether  in  the  organic  world  or  in  the  inorganic,  whether 
in  the  coal-beds  and  forests  of  the  earth,  or  in  the  brains 
and  muscles  of  men,  the  physical  philosopher  will  make 
good  his  right  to  investigate  them.  It  is  perfectly  vain  to 
attempt  to  stop  inquiry  as  to  the  actual  and  possible  actions 
of  matter  and  force.  Depend  upon  it,  if  a  chemist  by 
bringing  the  proper  materials  together,  in  a  retort  or 
crucible,  could  make  a  baby,  he  would  do  it.  There  is  no 
law,  moral  or  physical,  forbidding  him  to  do  it — his  in- 
quiries in  this  direction  are  limited  solely  by  his  own  ca- 
pacity and  the  laws  of  matter  and  force.  At  the  present 
moment  there  are,  no  doubt,  persons  experimenting  on 
the  possibility  of  producing  what  we  call  life  out  of  in- 
organic materials.  Let  them  pursue  their  studies  in  peace  ; 
it  is  only  by  such  trials  that  they  will  learn  the  limits  of 
their  powers. 

But  while  I  thus  make  the  largest  demand  for  freedom 
of  investigation — while  I  as  a  man  of  science  feel  a  natural 
pride  in  scientific  achievement,  while  I  regard  science  as  the 
most  powerful  instrument  of  intellectual  culture,  as  well  as 
the  most  powerful  ministrant  to  the  material  wants  of  men ; 
if  you  ask  me  whether  science  has  solved,  or  is  likely  in  our 
day  to  solve,  the  problem  of  this  universe,  I  must  shake  my 
head  in  doubt.  You  remember  the  first  Napoleon's  ques- 
tion, when  the  savans  who  accompanied  him  to  Egypt  dis- 
cussed in  his  presence  the  origin  of  the  universe,  and  solved 
it  to  their  own  apparent  satisfaction.  He  looked  aloft  to 


MATTER  AND   FORCE.  93 

the  starry  heavens,  and  said,  "  It  is  all  very  well,  gentle-  \ 
men  ;  but  who  made  all  these  ?  "  That  question  still  re-  j 
mains  unanswered,  and  science  makes  no  attempt  to  answer  j 
it.  As  far  as  I  can  see,  there  is  no  quality  in  the  human 
intellect  which  is  fit  to  be  applied  to  the  solution  of  the 
problem.  It  entirely  transcends  us.  The  mind  of  man  may 
be  compared  to  a  musical  instrument  with  a  certain  range 
of  notes,  beyond  which  in  both  directions  we  have  an 
infinitude  of  silence.  The  phenomena  of  matter  and  force 
lie  within  our  intellectual  range,  and  as  far  as  they  reach 
we  will  at  all  hazards  push  our  inquiries.  But  behind,  and 
above,  and  around  all,  the  real  mystery  of  this  universe  lies 
unsolved,  and,  as  far  as  we  are  concerned,  is  incapable  of 
solution.  Fashion  this  mystery  as  you  will,  with  that  I 
have  nothing  to  do.  But  be  careful  that  your  conception 
of  it  be  not  an  unworthy  one.  Invest  that  conception  with 
your  highest  and  holiest  thought,  but  be  careful  of  pre- 
tending to  know  more  about  it  than  is  given  to  man  to 
know.  Be  careful,  above  all  things,  of  professing  to  see  in 
the  phenomena  of  the  material  world  the  evidences  of  Di- 
vine pleasure  or  displeasure.  Doubt  those  who  would 
deduce  from  the  fall  of  the  tower  of  Siloam  the  anger  of  the 
Lord  against  those  who  were  crushed.  Doubt  those  equally 
who  pretend  to  see  in  cholera,  cattle-plague,  and  bad  har- 
vests, evidences  of  Divine'  anger.  Doubt  those  spiritual 
guides  who  in  Scotland  have  lately  propounded  the  mon- 
strous theory  that  the  depreciation  of  railway  scrip  is  a  con- 
sequence of  railway  travelling  on  a  Sunday.  Let  them  not, 
as  far  as  you  are  concerned,  label  and  libel  the  system  of 
Nature  with  their  ignorant  hypotheses.  Well  might  the 
mightiest  of  living  Scotchmen,  that  hero  of  the  intellect 
who  might  have  been  a  hero  in  the  field,  that  strong  and 
earnest  soul  who  has  made  every  soul  of  like  nature  in 
these  islands  his  debtor — looking  from  the  solitudes  of 
thought  into  this  highest  of  questions,  well,  I  say,  might 


94  FRAGMENTS  OF  SCIENCE. 

your  noble  old  Carlyle  scornfully  retort  on  such  interpreters 
of  the  ways  of  God  to  men  : 

The  Builder  of  this  universe  was  wise, 
He  formed  all  souls,  all  systems,  planets,  particles  ; 

The  plan  he  formed  his  worlds  and  JEons  by, 
Was — Heavens  ! — was  thy  small  nine-and-thirty  articles  ! 


V. 

ADDRESS  TO  THE  STUDENTS  OF  UNIVER- 
SITY COLLEGE,  LONDON, 

ON  THE  DISTRIBUTION  OF  PEIZES  IN  THE  FACULTY  OF  AETS. 

Session  1868-'69. 


"  Self-reverence,  self-knowledge,  self-control, 
These  three  alone  lead  life  to  sovereign  power, 
Yet  not  for  power  (power  of  herself 
Would  come  uncalled  for),  but  to  live  by  law, 
Acting  the  law  we  live  by  without  fear ; 
And,  because  right  is  right,  to  follow  right 
Were  wisdom  in  the  scorn  of  consequence." 

TENNYSON. 


Y. 

AN  ADDRESS    TO   STUDENTS. 

THEKE  is  an  idea  regarding  the  nature  of  man  which 
modern  philosophy  has  sought,  and  is  still  seeking,  to  raise 
into  clearness,  the  idea,  namely,  of  secular  growth.  Man 
is  not  a  thing  of  yesterday ;  nor  do  I  imagine  that  the 
slightest  controversial  tinge  is  imported  into  this  address 
when  I  say  that  he  is  not  a  thing  of  6,000  years  ago. 
Whether  he  came  originally  from  stocks  or  stones,  from 
nebulous  gas  or  solar  fire,  I  know  not ;  if  he  had  any  such 
origin  the  process  of  his  transformation  is  as  inscrutable  to 
you  and  to  me  as  that  of  the  grand  old  legend,  according 
to  which  "  the  Lord  God  formed  man  of  the  dust  of  the 
ground,  and  breathed  into  his  nostrils  the  breath  of  life ; 
and  man  became  a  living  soul."  But,  however  obscure 
man's  origin  may  be,  his  growth  is  not  to  be  denied.  Here 
a  little  and  there  a  little  added  through  the  ages  have 
slowly  transformed  him  from  what  he  was  into  what  he  is. 
The  doctrine  has  been  held  that  the  mind  of  the  child  is  like 
a  sheet  of  white  paper,  on  which  by  education  we  can  write 
what  characters  we  please.  This  doctrine  assuredly  needs 
qualification  and  correction.  In  physics,  when  an  external 
force  is  applied  to  a  body  with  a  view  of  affecting  its  inner 
texture,  if  we  wish  to  predict  the  result,  we  must  know 
whether  the  external  force  conspires  with  or  opposes  the 
internal  forces  of  the  body  itself;  and  in  bringing  the  influ- 
ence of  education  to  bear  upon  the  new-born  man  his  inner 
5 


98  FRAGMENTS  OF  SCIENCE. 

powers  must  be  also  taken  into  account.  He  conies  to  us 
as  a  bundle  of  inherited  capacities  and  tendencies,  labelled 
"  from  the  indefinite  past  to  the  indefinite  future  ; "  and  he 
makes  his  transit  from  the  one  to  the  other  through  the 
education  of  the  present  time.  The  object  of  that  educa- 
tion is,  or  ought  to  be,  to  provide  wise  exercise  for  his  ca- 
pacities, wise  direction  for  his  tendencies,  and  through  this 
exercise  and  this  direction  to  furnish  his  mind  with  such 
knowledge  as  may  contribute  to  the  usefulness,  the  beauty, 
and  the  nobleness  of  his  life. 

How  is  this  discipline  to  be  secured,  this  knowledge  im- 
parted ?  Two  rival  methods  now  solicit  attention — the  one 
organized  and  equipped,  the  labor  of  centuries  having  been 
expended  in  bringing  it  to  its  present  state  of  perfection  ; 
the  other,  more  or  less  chaotic,  but  becoming  daily  less  so, 
and  giving  signs  of  enormous  power,  both  as  a  source  of 
knowledge  and  as  a  means  of  discipline.  These  two 
methods  are  the  classical  and  the  scientific  method.  I  wish 
they  were  not  rivals ;  it  is  only  bigotry  and  short-sighted- 
ness that  make  them  so ;  for  assuredly  it  is  possible  to  give 
both  of  them  fair  play.  Though  hardly  authorized  to  ex- 
press any  opinion  whatever  upon  the  subject,  I  nevertheless 
hold  the  opinion  that  the  proper  study  of  a  language  is  an 
intellectual  discipline  of  the  highest  kind.  If  I  except  dis- 
cussions on  the  comparative  merits  of  popery  and  Protes- 
tantism, English  grammar  was  the  most  important  discipline 
of  my  boyhood.  The  piercing  through  the  involved  and 
inverted  sentences  of  "  Paradise  Lost ; "  the  linking  of  the 
verb  to  its  often  distant  nominative,  of  the  relative  to  its 
distant  antecedent,  of  the  agent  to  the  object  of  the  transi- 
tive verb,  of  the  preposition  to  the  noun  or  pronoun  which 
it  governed — the  study  of  variations  in  mood  and  tense,  the 
transformations  often  necessary  to  bring  out  the  true  gram- 
matical structure  of  a  sentence — all  this  was  to  my  young 
mind  a  discipline  of  the  highest  value,  and,  indeed,  a  source 


AN  ADDRESS  TO  STUDENTS.  99 

of  unflagging  delight.  How  I  rejoiced  when  I  found  a 
great  author  tripping,  and  was  fairly  able  to  pin  him  to  a 
corner  from  which  there  was  no  escape  !  As  I  speak,  some 
of  the  sentences  which  exercised  me  when  a  boy  rise  to  my 
recollection.  "  He  that  hath  ears  to  hear  let  him  hear." 
That  was  one  of  them,  where  the  "  He  "  is  left,  as  it  were, 
floating  in  mid  air  without  any  verb  to  support  it.  I  speak 
thus  of  English  because  it  was  of  real  value  to  me.  I  do 
not  speak  of  other  languages  because  their  educational  value 
for  me  was  almost  insensible.  But,  knowing  the  value  of 
English  so  well,  I  should  be  the  last  to  deny,  or  even  to 
doubt,  the  high  discipline  involved  in  the  proper  study  of 
Latin  and  Greek. 

That  study,  moreover,  has  other  merits  and  recommen- 
dations which  have  been  already  slightly  touched  upon. 
It  is  organized  and  systematized  by  long-continued  use. 
It  is  an  instrument  wielded -by  some  of  the  best  intellects 
of  the  country  in  the  education  of  youth ;  and  it  can  point 
to  results  in  the  achievements  of  our  foremost  men.  What, 
then,  has  science  to  offer  which  is  in  the  least  degree  likely  S 
to  compete  with  such  a  system  ?  I  cannot  better  reply 
than  by  recurring  to  the  grand  old  story  from  which  I  have  / 
already  quoted.  Speaking  of  the  world  and  all  that  therein 
is,  of  the  sky  and  the  stars  around  it,  the  ancient  writer 
says,  "  And  God  saw  all  that  he  had  made,  and  behold  it 
was  very  good."  It  is  the  body  of  things  thus  described  y 
which  science  offers  to  the  study  of  man.  There  is  a  very 
renowned  argument  much  prized  and  much  quoted  by 
theologians,  in  which  the  universe  is  compared  to  a  watch. 
Let  us  deal  practically  with  this  comparison.  Supposing  a 
watchmaker,  having  completed  his  instrument,  to  be  so 
satisfied  with  his  work  as  to  call  it  very  good,  what  would 
you  understand  him  to  mean?  You  would  not  suppose 
that  he  referred  to  the  dial-plate  in  front  and  the  chasing 
of  the  case  behind,  so  much  as  to  the  wheels  and  pinions, 


100  FRAGMENTS  OF  SCIENCE. 

the  springs  and  jewelled  pivots  of  the  works  within,  those 
qualities  and  powers,  in  short,  which  enable  the  watch  to 
perform  accurately  its  work  as  a  keeper  of  time.  With  re- 
gard to  the  knowledge  of  such  a  watch  he  would  be  a  mere 
ignoramus  who  would  content  himself  with  outward  inspec- 
tion. I  do  not  wish  to  say  one  severe  word  here  to-day, 
but  I  fear  that  many  of  those  who  are  very  loud  in  their 
praise  of  the  works  of  the  Lord  know  them  only  in  this  out- 
side and  superficial  way.  It  is  the  inner  works  of  the  uni- 
'  verse  which  science  reverently  uncovers ;  it  is  the  study  of 
these  that  she  recommends  as  a  discipline  worthy  of  all 
acceptation. 

The  ultimate  problem  of  physics  is  to  reduce  matter  by 
analysis  to  its  lowest  condition  of  divisibility,  and  force  to 
its  simplest  manifestations,  and  then  by  synthesis  to  con- 
struct from  these  elements  the  world  as  it  stands.  We  are 
still  a  long  way  from  the  final  solution  of  this  problem ; 
and  when  the  solution  comes,  it  will  be  one  more  of  spir- 
itual insight  than  of  actual  observation.  But  though  we 
are  still  a  long  way  from  this  complete  intellectual  mastery 
of  Nature,  we  have  conquered  vast  regions  of  it,  have 
learned  their  polities  and  the  play  of  their  powers.  We 
live  upon  a  ball  of  matter  eight  thousand  miles  in  diameter, 
swathed  by  an  atmosphere  of  unknown  height.  This  ball 
has  been  molten  by  heat,  chilled  to  a  solid,  and  sculptured 
by  water ;  it  is  made  up  of  substances  possessing  distinctive 
properties  and  modes  of  action,  properties  which  have  an 
immediate  bearing  upon  the  continuance  of  man  in  health, 
and  on  his  recovery  from  disease,  on  which  moreover  de- 
pend all  the  arts  of  industrial  life.  These  properties  and 
modes  of  action  offer  problems  to  the  intellect,  some  profit- 
able to  the  child,  and  others  sufficient  to  tax  the  highest 
powers  of  the  philosopher.  Our  native  sphere  turns  on  its 
axis  and  revolves  in  space.  It  is  one  of  a  band  which  do 
the  same.  It  is  illuminated  by  a  sun  which,  though  nearly 


AN  ADDRESS  TO  STUDENTS.  101 

a  hundred  millions  of  miles  distant,  can  be  brought  virtually 
into  our  closets  and  there  subjected  to  examination.  It 
has  its  winds  and  clouds,  its  rain  and  frost,  its  light,  heat, 
sound,  electricity,  and  magnetism.  And  it  has  its  vast 
kingdoms  of  animals  and  vegetables.  To  a  most  amazing 
extent  the  human  mind  has  conquered  these  things,  and 
revealed  the  logic  which  runs  through  them.  Were  they 
facts  only,  without  logical  relationship,  science  might,  as  a 
means  of  discipline,  suffer  in  comparison  with  language. 
But  the  whole  body  of  phenomena  is  instinct  with  law; 
the  facts  are  hung  on  principles,  and  the  value  of  physical 
science  as  a  means  of  discipline  consists  in  the  motion  of 
the  intellect,  both  inductively  and  deductively,  along  the 
lines  of  law  marked  out  by  phenomena.  As  regards  that 
discipline  to  which  I  have  already  referred  as  derivable 
from  the  study  of  languages — that,  and  more,  are  involved 
in  the  study  of  physical  science.  Indeed,  I  believe  it  would 
be  possible  so  to  limit  and  arrange  the  study  of  a  portion 
of  physics  as  to  render  the  mental  exercise  involved  in  it 
almost  qualitatively  the  same  as  that  involved  in  the  un- 
ravelling of  a  language. 

I  have  thus  far  limited  myself  to  the  purely  intellectual 
side  of  this  question.  But  man  is  not  all  intellect.  If  he 
were  so,  science  would,  I  believe,  be  his  proper  nutriment. 
But  he  feels  as  well  as  thinks ;  he  is  receptive  of  the  sub- 
lime and  the  beautiful  as  well  as  of  the  true.  Indeed,  I  be- 
lieve that  even  the  intellectual  action  of  a  complete  man  is, 
consciously  or  unconsciously,  sustained  by  an  under-current 
of  the  emotions.  It  is  vain,  I  think,  to  attempt  to  separate 
moral  and  emotional  nature  from  intellectual  nature.  Let 
a  man  but  observe  himself,  and  her  will,  if  I  mistake  not, 
find  that  in  nine  cases  out  of  ten,  moral  or  immoral  consid- 
erations, as  the  case  may  be,  are  the  motive  force  which 
pushes  his  intellect  into  action.  The  reading  of  the  works 
of  two  men,  neither  of  them  imbued  with  the  spirit  of 


102  FRAGMENTS  OF  SCIENCE. 

modern  science,  neither  of  them,  indeed,  friendly  to  that 
spirit,  has  placed  me  here  to-day.  These  men  are  the  Eng- 
lish Carlyle  and  the  American  Emerson.  I  must  ever  re- 
member with  gratitude  that  through  three  long,  cold  Ger- 
man winters  Carlyle  placed  me  in  my  tub,  even  when  ice 
was  on  its  surface,  at  five  o'clock  every  morning ;  not 
slavishly,  but  cheerfully,  meeting  each  day's  studies  with  a 
resolute  will,  determined  whether  victor  or  vanquished  not 
to  shrink  from  difficulty.  I  never  should  have  gone  through 
Analytical  Geometry  and  the  Calculus  had  it  not  been  for 
those  men.  I  never  should  have  become  a  physical  inves- 
tigator, and  hence  without  them  I  should  not  have  been 
here  to-day.  They  told  me  what  I  ought  to  do  in  a  way 
that  caused  me  to  do  it,  and  all  my  consequent  intellectual 
action  is  to  be  traced  to  this  purely  moral  source.  To  Car- 
lyle and  Emerson  I  ought  to  add  Fichte,  the  greatest  rep- 
resentative of  pure  idealism.  These  three  unscientific  men 
made  me  a  practical  scientific  worker.  They  called  out, 
"  Act !  "  I  hearkened  to  the  summons,  taking  the  liberty, 
however,  of  determining  for  myself  the  direction  which 
effort  was  to  take. 

And  I  may  now  cry,  "  Act ! "  but  the  potency  of  action 
must  be  yours.  I  may  pull  the  trigger,  but  if  the  gun  be 
not  charged  there  is  no  result.  We  are  creators  in  the 
intellectual  world  as  little  as  in  the  physical.  "We  may 
remove  obstacles,  and  render  latent  capacities  active,  but 
we  cannot  suddenly  change  the  nature  of  man.  The  "  new 
birth  "  itself  implies  the  preexistence  of  the  new  character 
which  requires  not  to  be  created  but  brought  forth.  You 
cannot  by  any  amount  of  missionary  labor  suddenly  trans- 
form the  savage  into  the  civilized  Christian.  The  improve- 
ment of  man  is  secular — not  the  work  of  an  hour  or  of  a 
day.  But  though  indubitably  bound  by  our  organizations, 
no  man  knows  what  the  potentialities  of  any  human  mind 
may  be,  which  require  only  release  to  be  brought  into  ac- 


AN  ADDRESS  TO  STUDENTS.  103 

tion.  Let  me  illustrate  this  point.  There  are  in  the  min- 
eral world  certain  crystals,  certain  forms,  for  instance,  of 
fluor-spar,  which  have  lain  darkly  in  the  earth  for  ages,  but 
which  nevertheless  have  a  potency  of  light  locked  up  within 
them.  In  their  case  the  potential  has  never  become  actual— 
the  light  is  in  fact  held  back  by  a  molecular  detent.  When 
these  crystals  are  warmed,  the  detent  is  lifted,  and  an  out- 
flow of  light  immediately  begins.  I  know  not  how  many 
of  you  may  be  in  the  condition  of  this  fluor-spar.  For  aught 
I  know,  every  one  of  you  may  be  in  this  condition,  requiring 
but  the  proper  agent  to  be  applied — the  proper  word  to  be 
spoken — to  remove  a  detent,  and  to  render  you  conscious 
of  light  within  yourselves  and  sources  of  light  to  others. 

The  circle  of  human  nature,  then,  is  not  complete  with- 
out the  arc  of  feeling  and  emotion.  The  lilies  of  the  field 
have  a  value  for  us  beyond  their  botanical  ones — a  certain 
lightening  of  the  heart  accompanies  the  declaration  that 
"  Solomon  in  all  his  glory  was  not  arrayed  like  one  of  these." 
The  sound  of  the  village  bell  which  comes  mellowed  from 
the  valley  to  the  traveller  upon  the  hill,  has  a  value  beyond 
its  acoustical  one.  The  setting  sun  when  it  mantles  with 
the  bloom  of  roses  the  alpine  snows,  has  a  value  beyond  its 
optical  one.  The  starry  heavens,  as  you  know,  had  for  Im- 
manuel  Kant  a  value  beyond  their  astronomical  one.  Round 
about  the  intellect  sweeps  the  horizon  of  emotions  from 
which  all  our  noblest  impulses  are  derived.  I  think  it  very 
desirable  to  keep  this  horizon  open ;  not  to  permit  either 
priest  or  philosopher  to  draw  down  his  shutters  between 
you  and  it.  And  here  the  dead  languages,  which  are  sure 
to  be  beaten  by  science  in  the  purely  intellectual  fight,  have 
an  irresistible  claim.  They  supplement  the  work  of  science 
by  exalting  and  refining  the  aesthetic  faculty,  and  must  on 
this  account  be  cherished  by  all  who  desire  to  see  human 
culture  complete.  There  must  be  a  reason  for  the  fascina- 
tion which  these  languages  have  so  long  exercised  upon 


104  FRAGMENTS  OF  SCIENCE. 

the  most  powerful  and  elevated  minds — a  fascination  which 
will  probably  continue  for  men  of  Greek  and  Romtta  mould 
to  the  end  of  time. 

In  connection  with  this  question  of  the  emotions  one 
very  obvious  danger  besets  many  of  the  more  earnest  spirits 
of  our  day — the  danger  of  haste  in  endeavoring  to  give  the 
feelings  repose.  We  are  distracted  by  systems  of  theology 
and  philosophy  which  were  taught  to  us  when  young,  and 
which  now  excite  in  us  -a  hunger  and  a  thirst  for  knowledge 
not  proved  to  be  attainable.  There  are  periods  when  the 
judgment  ought  to  remain  in  suspense,  the  data  on  which 
a  decision  might  be  based  being  absent.  This  discipline 
of  suspending  the  judgment  is  a  common  one  in  science, 
but  not  so  common  as  it  ought  to  be  elsewhere.  I  walked 
down  Regent  Street  some  time  ago  with  a  man  of  great 
gifts  and  acquirements,  discussing  with  him  various  theo- 
logical questions.  I  could  not  accept  his  views  of  the  origin 
and  destiny  of  the  universe,  nor  was  I  prepared  to  enun- 
ciate any  definite  viewrs  of  my  own.  He  turned  to  me  at 
length  and  said,  "  You  surely  must  have  a  theory  of  the 
universe."  That  I  should  in  one  way  or  another  have  solved 
this  mystery  of  mysteries  seemed  to  my  friend  a  matter  of 
course.  "  I  have  not  even  a  theory  of  magnetism,"  was  my 
reply.  We  ought  to  learn  to  wait,  and  pause  before  closing 
with  the  advances  of  those  expounders  of  the  ways  of  God 
to  men,  who  offer  us  intellectual  peace  at  the  modest  cost 
of  intellectual  life. 

The  teachers  of  the  world  ought  to  be  its  best  men,  and 
for  the  present  at  all  events  such  men  must  learn  self-trust. 
They  must  learn  more  and  more  to  do  without  external  aid ; 
save  such  aid  as  comes  from  the  contemplation  of  a  uni- 
verse, which,  though  it  baffles  the  intellect,  can  elevate  the 
heart.  But  they  must  learn  to  feel  the  mystery  of  that 
universe  without  attempting  to  give  it  a  rigid  form,  per- 
sonal or  otherwise.  By  the  fulness  and  freshness  of  their 


AN  ADDRESS  TO  STUDENTS.  105 

own  lives  and  utterances  they  must  awaken  life  in  othersX 
The  position  of  science  is  already  assured,  but  I  think  the  \ 
poet  also  will  have  a  great  part  to  play  in  the  future  of  the/ 
world.     To  him  it  is  given  for  a  long  time  to  come  to  fill 
those  shores  which  the  recession  of  the  theologic  tide  has 
left  exposed ;  to  him,  when  he  rightly  understands  his  mis- 
sion, and  does  not  flinch  from  the  tonic  discipline  which  it 
assuredly  demands,  we  have  a  right  to  look  for  that  height- 
ening and  brightening  of  life  which  so  many  of  us  need. 
He  ought  to  be  the  interpreter  of  that  power  which  as 

"  Jehovah,  Jove,  or  Lord," 

has  hitherto  filled  and  strengthened  the  human  heart. 

Let  me  utter  one  practical  word  in  conclusion — take 
care  of  your  health.  There  have  been  men  who  by  wise 
attention  to  this  point  might  have  risen  to  any  eminence  — 
might  have  made  great  discoveries,  written  great  poems, 
commanded  armies,  or  ruled  states,  but  who  by  unwise 
neglect  of  this  point  have  come  to  nothing.  Imagine  Her- 
cules as  oarsman  in  a  rotten  boat ;  what  can  he  do  there 
but  by  the  very  force  of  his  stroke  expedite  the  ruin  of  his 
craft.  Take  care  then  of  the  timbers  of  your  boat,  and 
avoid  all  practices  likely  to  introduce  either  wet  or  dry  rot 
among  them.  And  this  is  not  to  be  accomplished  by  desul- 
tory or  intermittent  efforts  of  the  will,  but  by  the  formation 
of  habits.  The  will  no  doubt  has  sometimes  to  put  forth 
its  strength  in  order  to  strangle  or  crush  the  special  tempta- 
tion. But  the  formation  of  right  habits  is  essential  to  your 
permanent  security.  They  diminish  your  chance  of  falling 
when  assailed,  and  they  augment  your  chance  of  recovery 
when  overthrown. 


VI. 

SCOPE   AND   LIMIT    OF    SCIENTIFIC 
MATERIALISM, 

AN  ADDRESS. 

DELIVERED   IN  THE  MATHEMATICAL  AND  PHYSICAL  SECTION  OF 
THE  BRITISH  ASSOCIATION  IN  NORWICH. 

August  19,  1868. 


"As  I  proceeded  I  found  my  philosopher  altogether  forsaking  mind 
or  any  other  principle  of  order,  and  having  recourse  to  air  and  ether,  and 
water,  and  other  eccentricities.  I  might  compare  him  to  a  person  who 
began  by  maintaining  generally  that  mind  is  the  cause  of  the  actions  of 
Socrates,  but  who,  when  he  endeavored  to  explain  the  cause  of  my  several 
actions  in  detail,  went  on  to  show  that  I  sit  here  because  my  body  is 
made  up  of  bones  and  muscles ;  and  the  bones  he  would  say  are  hard 
and  have  ligaments  which  divide  them,  and  the  muscles  are  elastic,  and 
they  cover  the  bones,  which  have  also  a  covering  or  environment  of  flesh 
and  skin  which  contains  them  ;  and  as  the  bones  are  lifted  at  their  joints 
by  the  contraction  or  relaxation  of  the  muscles,  I  am  able  to  bend  my 
limbs,  and  this  is  why  I  am  sitting  here  in  a  curved  posture ;  that  is 
what  he  would  say,  and  he  would  have  a  similar  explanation  of  my  talk- 
ing to  you,  which  he  would  attribute  to  sound,  and  air,  and  hearing,  and 
he  would  assign  ten  thousand  other  causes  of  the  same  sort,  forgetting  to 
mention  the  true  cause,  which  is  that  the  Athenians  have  thought  fit  to 
condemn  me,  and  accordingly  I  have  thought  it  better  and  more  right  to 
remain  here  and  undergo  my  sentence ;  for  I  am  inclined  to  think  that 
these  muscles  and  bones  of  mine  would  have  gone  off  to  Megara  or 
Boaotia — by  the  dog  of  Egypt  they  would,  if  they  had  been  guided  by 
their  own  idea  of  what  was  best,  and  if  I  had  not  chosen  as  the  better  and 
nobler  part,  instead  of  playing  truant  and  running  away,  to  undergo  any 
punishment  which  the  State  inflicts." — PLATO,  Jowctfs  Translation. 


VI. 

SCIENTIFIC  MATERIALISM. 

THE  CELEBRATED  FiCHTE,  in  his  lectures  on  the  "Vo- 
cation of  the  Scholar,"  insisted  on  a  culture  which  should 
not  be  one-sided,  but  all-sided.  The  scholar's  intellect 
was  to  expand  spherically  and  not  in  a  single  direction 
only.  In  one  direction,  however,  Fichte  required  that 
the  scholar  should  apply  himself  directly  to  Nature,  be- 
come a  creator  of  knowledge,  and  thus  repay  by  original 
labors  of  his  own  the  immense  debt  he  owed  to  the 
labors  of  others.  It  was  these  which  enabled  him  to  sup- 
plement the  knowledge  derived  from  his  own  researches, 
so  as  to  render  his  culture  rounded  and  not  one-sided. 

As  regards  science  Fichte's  idea  is  to  some  extent 
illustrated  by  the  constitution  and  the  labors  of  the  British 
Association.  We  have  a  body  of  men  engaged  in  the 
pursuit  of  Natural  Knowledge,  but  variously  engaged^ 
While  sympathizing  with  each  of  its  departments,  and 
supplementing  his  culture  by  knowledge  drawn  from  all 
of  them,  each  student  among  us  selects  one  subject  for  the 
exercise  of  his  own  original  faculty — one  line  along  which 
he  may  carry  the  light  of  his  private  intelligence  a  little 
way  into  the  darkness  by  which  all  knowledge  is  sur- 
rounded. Thus,  the  geologist  deals  with  the  rocks ;  the 
biologist  with  the  conditions  and  phenomena  of  life ;  the 
astronomer  with  stellar  masses  and  motions ;  the  mathe- 
matician with  the  relations  of  space  and  number;  the 


110  FRAGMENTS  OF  SCIENCE. 

chemist  pursues  his  atoms,  while  the  physical  investigator 
has  his  own  large  field  in  optical,  thermal,  electrical, 
acoustical,  and  other  phenomena.  The  British  Associa- 
tion then,  as  a  whole,  faces  physical  Nature  on  all  sides 
and  pushes  knowledge  centrifugally  outward,  the  sum  of 
its  labors  constituting  what  Fichte  might  call  the  sphere  of 
natural  knowledge.  In  the  meetings  of  the  Association  it 
is  found  necessary  to  resolve  this  sphere  into  its  component 
parts,  which  take  concrete  form  under  the  respective  letters 
of  our  Sections. 

This  is  the  Mathematical  and  Physical  Section.  Mathe- 
matics and  physics  have  been  long  accustomed  to  coalesce. 
For,  no  matter  how  subtle  a  natural  phenomenon  may  be, 
whether  we  observe  it  in  the  region  of  sense,  or  follow  it 
into  that  of  imagination,  it  is  in  the  long-run  reducible  to 
mechanical  laws.  But  the  mechanical  data  once  guessed 
or  given,  mathematics  become  all-powerful  as  an  instru- 
ment of  deduction.  The  command  of  geometry  over  the 
relations  of  space,  the  far-reaching  power  which  organized 
symbolic  reasoning  confers,  are  potent  both  as  means  of 
physical  discovery,  and  of  reaping  the  entire  fruits  of  dis- 
covery. Indeed,  without  mathematics,  expressed  or  im- 
plied, our  knowledge  of  physical  science  would  be  friable 
in  the  extreme. 

Side  by  side  with  the  mathematical  method  we  have 
the  method  of  experiment.  Here,  from  a  starting-point 
furnished  by  his  own  researches,  or  those  of  others,  the  in- 
vestigator proceeds  by  combining  intuition  and  verification. 
He  ponders  the  knowledge  he  possesses  and  tries  to  push 
it  further,  he  guesses  and  checks  his  guess,  he  conjectures 
and  confirms  or  explodes  his  conjecture.  These  guesses 
and  conjectures  are  by  no  means  leaps  in  the  dark ;  for 
knowledge  once  gained  casts  a  faint  light  beyond  its  own 
immediate  boundaries.  There  is  no  discovery  so  limited 
as  not  to  illuminate  something  beyond  itself.  The  force 


SCIENTIFIC  MATERIALISM.  Ill 

of  intellectual  penetration  into  this  penumbral  region  which 
surrounds  actual  knowledge  is  not,  as  some  seem  to  think, 
dependent  upon  method,  but  upon  the  genius  of  the  in- 
vestigator. There  is,  however,  no  genius  so  gifted  as  not 
to  need  control  and  verification.  The  profoundest  minds 
know  best  that  Nature's  ways  are  not  at  all  times  their 
ways,  and  that  the  brightest  flashes  in  the  world  of 
thought  are  incomplete  until  they  have  been  proved  to 
have  their  counterparts  in  the  world  of  fact.  Thus  the^ 
vocation  of  the  true  experimentalist  may  be  defined  as 
the  continued  exercise  of  spiritual  insight,  and  its  inces- 
sant correction  and  realization.  His  experiments  consti- 
tute a  body,  of  which  his  purified  intuitions  are,  as  it  were, 
the  soul. 

Partly  through  methematical  and  partly  through  ex- 
perimental research,  physical  science  has  of  late  years  as- 
sumed a  momentous  position  in  the  world.  Both  in  a 
material  and  in  an  intellectual  point  of  view  it  has  pro- 
duced, and  it  is  destined  to  produce,  immense  changes — 
vast  social  ameliorations,  and  vast  alterations  in  the  popu- 
lar conception  of  the  origin,  rule,  and  governance  of  natural 
things.  By  science,  in  the  physical  world,  miracles  are 
wrought,  while  philosophy  is  forsaking  its  ancient  meta- 
physical channels  and  pursuing  others  which  have  been 
opened  or  indicated  by  scientific  research.  This  must  be- 
come more  and  more  the  case  as  philosophical  writers 
become  more  deeply  imbued  with  the  methods  of  science, 
better  acquainted  with  the  facts  which  scientific  men  have 
won,  and  with  the  great  theories  which  they  have  elaborated. 

If  you  look  at  the  face  of  a  watch,  you  see  the  hour 
and  minute  hands,  and  possibly  also  a  second-hand,  moving 
over  the  graduated  dial.  Why  do  these  hands  move  ?  and 
why  are  their  relative  motions  such  as  they  are  observed 
to  be  ?  These  questions  cannot  be  answered  without  open- 
ing  the  watch,  mastering  its  various  parts,  and  ascertaining 


112  FRAGMENTS  OF  SCIENCE. 

their  relationship  to  each  other.  When  this  is  done,  we 
find  that  the  observed  motion  of  the  hands  follows  of  ne- 
cessity from  the  inner  mechanism  of  the  watch,  when  acted 
upon  by  the  force  invested  in  the  spring. 

The  motion  of  the  hands  may  be  called  a  phenomenon 
of  art,  but  the  case  is  similar  with  the  phenomena  of  Nature. 
These  also  have  their  inner  mechanism,  and  their  store  of 
force  to  set  that  mechanism  going.  The  ultimate  problem 
of  physical  science  is  to  reveal  this  mechanism,  to  discern 
this  store,  and  to  show  that  from  the  combined  action  of 
both  the  phenomena  of  which  they  constitute  the  basis 
must  of  necessity  flow. 

I  thought  an  attempt  to  give  you  even  a  brief  and 
sketchy  illustration  of  the  manner  in  which  scientific  think- 
ers regard  this  problem  would  not  be  uninteresting  to  you 
on  the  present  occasion ;  more  especially  as  it  will  give  me 
occasion  to  say  a  word  or  two  on  the  tendencies  and  limits 
of  modern  science ;  to  point  out  the  region  which  men  of 
science  claim  as  their  own,  and  where  it  is  mere  waste  of 
time  to  oppose  their  advance,  and  also  to  define,  if  possible, 
the  bourne  between  this  and  that  other  region  to  which 
the  questionings  and  yearnings  of  the  scientific  intellect 
are  directed  in  vain. 

But  here  your  tolerance  will  be  needed.  It  was  the 
American  Emerson,  I  think,  who  said  that  it  is  hardly  pos- 
sible to  state  any  truth  strongly  without  apparent  injustice 
to  some  other  truth.  Truth  is  often  of  a  dual  character, 
taking  the  form  of  a  magnet  with  two  poles  ;  and  many  of 
the  differences  which  agitate  the  thinking  part  of  mankind 
are  to  be  traced  to  the  exclusiveness  with  which  partisan 
reasoners  dwell  upon  one-half  of  the  duality  in  forgetfulness 
of  the  other.  The  proper  course  appears  to  be  to  state 
both  halves  strongly,  and  allow  each  its  fair  share  in  the 
formation  of  the  resultant  conviction.  But  this  waiting  for 
the  statement  of  the  two  sides  of  a  question  implies  pa- 


SCIENTIFIC  MATERIALISM.  113 

tience.  It  implies  a  resolution  to  suppress  indignation  if 
the  statement  of  the  one-half  should  clash  with  our  convic- 
tions, and  to  repress  equally  undue  elation  if  the  half-state- 
ment should  happen  to  chime  in  with  our  views.  It  implies 
a  determination  to  wait  calmly  for  the  statement  of  the 
whole,  before  we  pronounce  judgment  in  the  form  of  either 
acquiescence  or  dissent. 

This  premised,  and,  I  trust,  accepted,  let  us  enter  upon 
our  task.  There  have  been  writers  who  affirmed  that  the 
pyramids  of  Egypt  were  the  productions  of  Nature  ;  and  in 
his  early  youth  Alexander  von  Humboldt  wrote  a  learned 
essay  with  the  express  object  of  refuting  this  notion.  We 
now  regard  the  pyramids  as  the  work  of  men's  hands,  aided 
probably  by  machinery  of  which  no  record  remains.  We 
picture  to  ourselves  the  swarming  workers  toiling  at  those 
vast  erections,  lifting  the  inert  stones,  and,  guided  by  the 
volition,  the  skill,  and  possibly  at  times  by  the  whip  of  the 
architect,  placing  them  in  their  proper  positions.  The 
blocks  in  this  case  were  moved  and  posited  by  a  power 
external  to  themselves,  and  the  final  form  of  the  pyramid 
expressed  the  thought  of  its  human  builder. 

Let  us  pass  from  this  illustration  of  constructive  power 
to  another  of  a  different  kind.  When  a  solution  of  common 
salt  is  slowly  evaporated,  the  water  which  holds  the  salt 
in  solution  diappears,  but  the  salt  itself  remains  behind.  At 
a  certain  stage  of  concentration  the  salt  can  no  longer  retain 
the  liquid  form ;  its  particles,  or  molecules,  as  they  are 
called,  begin  to  deposit  themselves  as  minute  solids,  so 
minute,  indeed,  as  to  defy  all  microscopic  power.  As  evapo- 
ration continues  solidification  goes  on,  and  we  finally  obtain, 
through  the  clustering  together  of  innumerable  molecules, 
a  finite  crystalline  mass  of  a  definite  form.  What  is  this 
form  ?  It  sometimes  seems  a  mimicry  of  the  architecture 
of  Egypt.  We  have  little  pyramids  built  by  the  salt, 
terrace  above  terrace  from  base  to  apex,  forming  a  series  of 


114  FRAGMENTS  OF  SCIENCE. 

steps  resembling  those  up  which  the  Egyptian  traveller  is 
dragged  by  his  guides.  The  human  mind  is  as  little  dis- 
posed to  look  unquestioning  at  these  pyramidal  salt-crys- 
tals as  to  look  at  the  pyramids  of  Egypt  without  inquiring 
whence  they  came.  How,  then,  are  those  salt-pyramids 
built  up  ? 

Guided  by  analogy,  you  may,  if  you  like,  suppose  that 
swarming  among  the  constituent  molecules  of  the  salt, 
there  is  an  invisible  population,  controlled  and  coerced  by 
some  invisible  master,  and  placing  the  atomic  blocks  in 
their  positions.  This,  however,  is  not  the  scientific  idea, 
nor  do  I  think  your  good  sense  will  accept  it  as  a  likely 
one.  The  scientific  idea  is  that  the  molecules  act  upon  each 
other  without  the  intervention  of  slave  labor ;  that  they 
attract  each  other  and  repel  each  other  at  certain  definite 
points,  or  poles,  and  in  certain  definite  directions  ;  and  that 
the  pyramidal  form  is  the  result  of  this  play  of  attraction 
and  repulsion.  While,  then,  the  blocks  of  Egypt  were  laid 
down  by  a  power  external  to  themselves,  these  molecular 
blocks  of  salt  are  self-posited,  being  fixed  in  their  places  by 
the  forces  with  which  they  act  upon  each  other. 

I  take  common  salt  as  an  illustration  because  it  is  so 
familiar  to  us  all ;  but  any  other  crystalline  substance  would 
answer  my  purpose  equally  well.  Everywhere,  in  fact, 
throughout  inorganic  Nature,  we  have  this  formative  power, 
as  Fichte  would  call  it — this  structural  energy  ready  to 
come  into  play,  and  build  the  ultimate  particles  of  matter 
into  definite  shapes.  The  ice  of  our  winters  and  of  our 
polar  regions  is  its  handywork,  and^  so  equally  are  the 
quartz,  felspar,  and  mica  of  our  rocks.\  Our  chalk-beds  are 
for  the  most  part  composed  of  minute  shells,  which  are  also 
the  product  of  structural  energy ;  but,  behind  the  shell,  as 
a  whole,  lies  a  more  remote  and  subtle  formative  act.  These 
shells  are  built  up  of  little  crystals  of  calc-spar,  and  to  form 
these  crystals  the  structural  force  had  to  deal  with  the 


SCIENTIFIC  MATERIALISM.  115 

intangible  molecules  of  carbonate  of  lime.  This  tendency 
on  the  part  of  matter  to  organize  itself,  to  grow  into  shape, 
to  assume  definite  forms  in  obedience  to  the  definite  action 
of  force,  is,  as  I  have  said,  all-pervading.  It  is  in  the 
ground  on  which  you  tread,  in  the  water  you  drink,  in  the 
air  you  breathe.  Incipient  life,  as  it  were,  manifests  itself 
throughout  the  whole  of  what  we  call  inorganic  Nature. 

The  forms  of  the  minerals  resulting  from  this  play  of 
polar  forces  are  various,  and  exhibit  different  degrees  of 
complexity.  Men  of  science  avail  themselves  of  all  possible 
means  of  exploring  their  molecular  architecture.  For  this 
purpose  they  employ  in  turn  as  agents  of  exploration,  light, 
heat,  magnetism,  electricity,  and  sound.  Polarized  light  is 
especially  useful  and  powerful  here.  A  beam  of  such  light, 
when  sent  in  among  the  molecules  of  a  crystal,  is  acted  on 
by  them,  and  from  this  action  we  infer  with  more  or  less  of 
clearness  the  manner  in  which  the  molecules  are  arranged. 
That  differences,  for  example,  exist  between  the  inner 
structure  of  rock-salt  and  crystallized  sugar  or  sugar-candy, 
is  thus  strikingly  revealed.  These  actions  often  display 
themselves  in  chromatic  phenomena  of  great  splendor,  the 
play  of  molecular  force  being  so  regulated  as  to  remove 
some  of  the  colored  constituents  of  white  light,  and  to  leave 
others  with  increased  intensity  behind. 

And  now  let  us  pass  from  what  we  are  accustomed  to 
regard  as  a  dead  mineral  to  a  living  grain  of  corn.  When 
it  is  examined  by  polarized  light,  chromatic  phenomena 
similar  to  those  noticed  in  crystals  are  observed.  And 
why  ?  Because  the  architecture  of  the  grain  resembles  the 
architecture  of  the  crystal.  In  the  grain  also  the  molecules 
are  set  in  definite  positions,  and  in  accordance  with  their 
arrangement  they  act  upon  the  light.  But  what  has  built 
together  the  molecules  of  the  corn  ?  I  have  already  said 
regarding  crystalline  architecture  that  you  may,  if  you 
please,  consider  the  atoms  and  molecules  to  be  placed  in 


116  FRAGMENTS  OF  SCIENCE. 

position  by  a  power  external  to  themselves.  The  same 
hypothesis  is  open  to  you  now.  But  if  in  the  case  of  crys- 
tals you  have  rejected  this  notion  of  an  external  architect, 
I  think  you  are  bound  to  reject  it  now,  and  to  conclude 
that  the  molecules  of  the  corn  are  self-posited  by  the  forces 
with  which  they  act  upon  each  other.  It  would  be  poor 
philosophy  to  invoke  an  external  agent  in  the  one  case  and 
to  reject  it  in  the  other. 

Instead  of  cutting  our  grain  of  corn  into  slices  and  sub- 
jecting it  to  the  action  of  polarized  light,  let  us  place  it  in 
the  earth  and  subject  it  to  a  certain  degree  of  warmth.  In 
other  words,  let  the  molecules,  both  of  the  corn  and  of  the 
surrounding  earth,  be  kept  in  that  state  of  agitation  which 
we  call  warmth.  Under  these  circumstances,  the  grain  and 
the  substances  which  surround  it  interact,  and  a  definite 
molecular  architecture  is  the  result.  A  bud  is  formed ;  this 
bud  reaches  the  surface,  where  it  is  exposed  to  the  sun's 
rays,  which  are  also  to  be  regarded. as  a  kind  of  vibratory 
motion.  And  as  the  motion  of  common  heat  with  which 
the  grain  and  the  substances  surrounding  it  were  first 
endowed,  enabled  the  grain  and  these  substances  to  exer- 
cise their  attractions  and  repulsions,  and  thus  to  coalesce 
in  definite  forms,  so  the  specific  motion  of  the  sun's  rays 
now  enables  the  green  bud  to  feed  upon  the  carbonic  acid 
and  the  aqueous  vapor  of  the  air.  The  bud  appropriates 
those  constituents  of  both  for  which  it  has  an  elective 
attraction,  and  permits  the  other  constituent  to  resume  its 
place  in  the  air.  Thus  the  architecture  is  carried  on. 
Forces  are  active  at  the  root,  forces  are  active  in  the  blade, 
the  matter  of  the  earth  and  the  matter  of  the  atmosphere 
are  drawn  toward  the  root  and  blade,  and  the  plant  aug- 
ments in  size.  We  have  in  succession  the  bud,  the  stalk, 
the  ear,  the  full  corn  in  the  ear;  the  cycle  of  molecular 
action  being  completed  by  the  production  of  grains  similar 
to  that  with  which  the  process  began. 


SCIENTIFIC  MATERIALISM.  117 

Now  there  is  nothing  in  this  process  which  necessarily 
eludes  the  conceptive  or  imagining  power  of  the  purely 
human  mind.  An  intellect  the  same  in  kind  as  our  own 
would,  if  only  sufficiently  expanded,  be  able  to  follow  the 
whole  process  from  beginning  to  end.  It  would  see  every 
molecule  placed  in  its  position  by  the  specific  attractions 
and  repulsions  exerted  between  it  and  other  molecules,  the 
whole  process  and  its  consummation  being  an  instance  of 
the  play  of  molecular  force.  Given  the  grain  and  its  envi- 
ronment, the  purely  human  intellect  might,  if  sufficiently 
expanded,  trace  out  a  priori  every  step  of  the  process  of 
growth,  and  by  the  application  of  purely  mechanical  prin- 
ciples demonstrate  that  the  cycle  must  end,  as  it  is  seen  to 
end,  in  the  reproduction  of  forms  like  that  with  which  it 
began.  A  similar  necessity  rules  here  to  that  which  rules 
the  planets  in  their  circuits  round  the  sun. 

You  will  notice  that  I  am  stating  my  truth  strongly,  as 
at  the  beginning  we  agreed  it  should  be  stated.  But  I 
must  go  still  further,  and  affirm  that  in  the  eye  of  science 
the  animal  body  is  just  as  much  the  product  of  molecular 
force  as  the  stalk  and  ear  of  corn,  or  as  the  crystal  of  salt 
or  sugar.  Many  of  the  parts  of  the  body  are  obviously 
mechanical.  Take  the  human  heart,  for  example,  with  its 
system  of  valves,  or  take  the  exquisite  mechanism  of  the 
eye  or  hand.  Animal  heat,  moreover,  is  the  same  in  kind 
as  the  heat  of  a  fire,  being  produced  by  the  same  chemical 
process.  Animal  motion,  too,  is  as  directly  derived  from 
the  food  of  the  animal,  as  the  motion  of  Trevethyck's  walk- 
ing-engine from  the  fuel  in  its  furnace.  As  regards  matter, 
the  animal  body  creates  nothing ;  as  regards  force,  it  creates 
nothing.  Which  of  you  by  taking  thought  can  add  one 
cubit  to  his  stature  ?  All  that  has  been  said,  then,  regard- 
ing the  plant  may  be  restated  with  regard  to  the  animal. 
Every  particle  that  enters  into  the  composition  of  a  muscle, 
a  nerve,  or  a  bone,  has  been  placed  in  its  position  by  mo- 


118  FRAGMENTS  OF  SCIENCE. 

lecular  force.  And  unless  the  existence  of  law  in  these 
matters  be  denied,  and  the  element  of  caprice  introduced, 
we  must  conclude  that,  given  the  relation  of  any  molecule 
of  the  body  to  its  environment,  its  position  in  the  body 
might  be  determined  mathematically.  Our  difficulty  is  not 
with  the  quality  of  the  problem,  but  with  its  complexity  • 
and  this  difficulty  might  be  met  by  the  simple  expansion 
of  the  faculties  which  we  now  possess.  Given  this  expan- 
sion, with  the  necessary  molecular  data,  and  the  chick 
might  be  deduced  as  rigorously  and  as  logically  from  the 
egg  as  the  existence  of  Neptune  from  the  disturbances  of 
Uranus,  or  as  conical  refraction  from  the  undulatory  theory 
L  of  light. 

You  see  I  am  not  mincing  matters,  but  avowing  nakedly 
what  many  scientific  thinkers  more  or  less  distinctly  be- 
lieve. The  formation  of  a  crystal,  a  plant,  or  an  animal,  is 
in  their  eyes  a  purely  mechanical  problem,  which  differs 
from  the  problems  of  ordinary  mechanics  in  the  smallness 
of  the  masses  and  the  complexity  of  the  processes  involved. 
Here  you  have  one  half  of  our  dual  truth ;  let  us  now  glance 
at  the  other  half.  Associated  with  this  wonderful  mechan- 
ism of  the  animal  body  we  have  phenomena  no  less  certain 
than  those  of  physics,  but  between  which  and  the  mechan- 
ism we  discern  no  necessary  connection.  A  man,  for  ex- 
ample, can  say,  I  feel,  I  thinJc,  I  love  ;  but  how  does 
consciousness  infuse  itself  into  the  problem  ?  The  human 
brain  is  said  to  be  the  organ  of  thought  and  feeling ;  when 
we  are  hurt  the  brain  feels  it,  when  we  ponder  it  is  the 
brain  that  thinks,  when  our  passions  or  affections  are  ex- 
cited it  is  through  the  instrumentality  of  the  brain.  Let  us 
endeavor  to  be  a  little  more  precise  here.  I  hardly  imagine 
there  exists  a  profound  scientific  thinker,  who  has  reflected 

I  upon  the  subject,  unwilling  to  admit  the  extreme  proba- 
bility of  the  hypothesis  that,  for  every  fact  of  consciousness, 
whether  in  the  domain  of  sense,  of  thought,  or  of  emotion, 


SCIENTIFIC   MATERIALISM.  119 

a  definite  molecular  condition  of  motion  or  structure  is  set 
up  in  the  brain ;  or  who  would  be  disposed  even  to  deny 
that  if  the  motion  or  structure  be  induced  by  internal 
causes  instead  of  external,  the  effect  on  consciousness  will 
be  the  same  ?  Let  any  nerve,  for  example,  be  thrown  by 
morbid  action  into  the  precise  state  of  motion  which  would 
be  communicated  to  it  by  the  pulses  of  a  heated  body, 
surely  that  nerve  will  declare  itself  hot — the  mind  will 
accept  the  subjective  intimation  exactly  as  if  it  were  ob- 
jective. The  retina  may  be  excited  by  purely  mechanical 
means.  A  blow  on  the  eye  causes  a  luminous  flash,  and 
the  mere  pressure  of  the  finger  on  the  external  ball  pro- 
duces a  star  of  light,  which  Newton  compared  to  the  circles 
on  a  peacock's  tail.  Disease  makes  people  see  visions  and 
dream  dreams ;  but,  in  all  such  cases,  could  we  examine 
the  organs  implicated,  we  should,  on  philosophical  grounds, 
expect  to  find  them  in  that  precise  molecular  condition 
which  the  real  objects,  if  present,  would  superinduce. 

The  relation  of  physics  to  consciousness  being  thus 
invariable,  it  follows  that,  given  the  state  of  the  brain,  the 
corresponding  thought  or  feeling  might  be  inferred ;  or 
given  the  thought  or  feeling,  the  corresponding  state  of  the 
brain  might  be  inferred.  But  how  inferred  ?  It  would  be 
at  bottom  not  a  case  of  logical  inference  at  all,  but  of 
empirical  association.  You  may  reply  that  many  of  the 
inferences  of  science  are  of  this  character ;  the  inference, 
for  example,  that  an  electric  current  of  a  given  direction 
will  deflect  a  magnetic  needle  in  a  definite  way ;  but  the 
cases  differ  in  this,  that  the  passage  from  the  current  to  the 
needle,  if  not  demonstrable,  is  thinkable,  and  that  we  enter- 
tain no  doubt  as  to  the  final  mechanical  solution  of  the 
problem.  But  the  passage  from  the  physics  of  the  brain 
to  the  corresponding  facts  of  consciousness  is  unthinkable. 
Granted  that  a  definite  thought,  and  a  definite  molecular  7 
action  in  the  brain  occur  simultaneously ;  we  do  not  possess 


120  FRAGMENTS  OF  SCIENCE. 

the  intellectual  organ,  nor  apparently  any  rudiment  of  the 
organ,  which  would  enable  us  to  pass,  by  a  process  of  rea- 
i  soning,  from  the  one  to  the  other.  They  appear  together, 
I  but  we  do  not  know  why.  Were  our  minds  and  senses  so 
expanded,  strengthened,  and  illuminated  as  to  enable  us  to 
see  and  feel  the  very  molecules  of  the  brain ;  were  we 
capable  of  following  all  their  motions,  all  their  groupings, 
all  their  electric  discharges,  if  such  there  be  ;  and  were  we 
intimately  acquainted  with  the  corresponding  states  of 
thought  and  feeling,  we  should  be  as  far  as  ever  from  the 
solution  of  the  problem,  "  How  are  these  physical  processes 
I  connected  with  the_facts  of  consciousness  ?  "  The  chasm 
between  the  two  classes  of  phenomena  would  still  remain 
intellectually  impassable.  Let  the  consciousness  of  love, 
for  example,  be  associated  with  a  right-handed  spiral 
motion  of  the  molecules  of  the  brain,  and  the  consciousness 
of  hate  with  a  left-handed  spiral  motion.  "We  should  then 
know  when  we  love  that  the  motion  is  in  one  direction, 
and  when  we  hate  that  the  motion  is  in  the  other ;  but  the 
"  WHY  ?  "  would  remain  as  unanswerable  as  before. ' 

'r""ln  affirming  that  the  growth  of  the  body  is  mechanical, 
and  that  thought,  as  exercised  by  us,  has  its  correlative  in 
the  physics  of  the  brain,  I  think  the  position  of  the  "  Ma- 
terialist" is  stated,  as  far  as  that  position  is  a  tenable 
one.  I  think  the  materialist  will  be  able  finally  to  main- 
tain this  position  against  all  attacks  ;  but  I  do  not  think, 
in  the  present  condition  of  the  human  mind,  that  he  can 
pass  beyond  this  position.  I  do  not  think  he  is  entitled 
to  say  that  his  molecular  groupings  and  his  molecular 
motions  explain  every  thing.  In  reality,  they  explain 
nothing.  The  utmost  he  can  affirm  is  the  association  of 
two  classes  of  phenomena,  of  whose  real  bond  of  union 
he  is  in  absolute  ignorance.  The  problem  of  the  con- 
nection of  body  and  soul  is  as  insoluble  in  its  modern 
form  as  it  was  in  the  prescientific  ages.  Phosphorus  is 


SCIENTIFIC  MATERIALISM.  121 

known  to  enter  into  the  composition  of  the  human  brain, 
and  a  trenchant  German  writer  has  exclaimed, -^-Ohrre  • 
Phespht3iy^eift-Gedaiikez"  That  may  or  may  not  be  the 
case ;  but  even  if  we  knew  it  to  be  the  case,  the  knowledge 
would  not  lighten  our  darkness.  On  both  sides  of  the  zone 
here  assigned  to  the  materialist  he  is  equally  helpless.  If 
you  ask  him  whence  is  this  "  Matter  "  of  which  we  have 
been  discoursing,  who  or  what  divided  it  into  molecules, 
who  or  what  impressed  upon  them  this  necessity  of  running 
into  organic  forms,  he  has  no  answer.  Science  is  mute  in 
reply  to  these  questions.  But  if  the  materialist  is  con- 
founded and  science  rendered  dumb,  who  else  is  prepared 
with  a  solution  ?  To  whom  has  this  arm  of  the  Lord  been 
revealed?  Let  us  lower  our  heads  and  acknowledge  our 
ignorance,  priest  and  philosopher,  one  and  all. 

Perhaps  the  mystery  may  resolve  itself  into  knowledge 
nt  some  future  day.  The  process  of  things  upon  this  earth 
has  been  one  of  amelioration.  It  is  a  long  way  from  the 
Iguanodon  and  his  contemporaries  to  the  President  and 
members  of  the  British  Association.  And  whether  we  re- 
gard the  improvement  from  the  scientific  or  from  the  theo- 
logical point  of  view,  as  the  result  of  progressive  develop- 
ment, or  as  the  result  of  successive  exhibitions  of  creative 
energy,  neither  view  entitles  us  to  assume  that  man's  present 
faculties  end  the  series — that  the  process  of  amelioration 
stops  at  him.  A  time  may  therefore  come  when  this  ultra- 
scientific  region  by  which  we  are  now  enfolded  may  offer  it- 
self to  terrestrial,  if  not  to  human  investigation.  Two-thirds 
of  the  rays  emitted  by  the  sun  fail  to  arouse  in  the  eye  the 
sense  of  vision.  The  rays  exist,  but  the  visual  organ  requi- 
site for  their  translation  into  light  does  not  exist.  And  so 
from  this  region  of  darkness  and  mystery  which  surrounds 
us,  rays  may  now  be  darting  which  require  but  the  develop- 
ment of  the  proper  intellectual  organs  to  translate  them 
into  knowledge  as  far  surpassing  ours  as  ours  surpasses 
G 


122  FRAGMENTS  OF  SCIENCE. 

that  of  the  wallowing  reptiles  which  once  held  possession 
gf  this  planet.  Meanwhile  the  mystery  is  not  without  its 
uses.  It  certainly  may  be  made  a  power  in  the  human  soul ; 
but  it  is  a  power  which  has  feeling,  not  knowledge,  for  its 
base.  It  may  be,  and  will  be,  and  I  hope  is,  turned  to 
account,  both  in  studying  and  strengthening  the  intellect, 
and  in  rescuing  man  from  that  littleness  to  which,  in  the 
struggle  for  existence,  or  for  precedence  in  the  world,  he 
is  continually  prone. 


Musings  on  the  Matterliorn,  .July  27, 1868. 

"  HACKED  and  hurt  by  time,  the  aspect  of  the  mountain  from  its 
higher  crags  saddened  me.  Hitherto  the  impression  it  made  was  that  of 
savage  strength  ;  here  we  had  inexorable  decay.  But  this  notion  of  decay 
implied  a  reference  to  a  period  when  the  Matterhora  was  in  the  full 
strength  of  mountainhood.  Thought  naturally  ran  back  to  its  remoter 
origin  and  sculpture.  Nor  did  thought  halt  there,  but  wandered  on 
through  molten  worlds  to  that  nebulous  haze  which  philosophers  have 
regarded,  and  with  good  reason,  as  the  proximate  source  of  all  material 
things.  I  tried  to  look  at  this  universal  cloud,  containing  within  itself  the 
prediction  of  all  that  has  since  occurred ;  I  tried  to  imagine  it  as  the  seat 
of  those  forces  whose  action  was  to  issue  in  solar  and  stellar  systems, 
and  all  that  they  involve.  Did  that  formless  fog  contain  potentially  the 
sadness  with  which  I  regarded  the  Matterhorn  ?  Did  the  thought  which 
now  ran  back  to  it  simply  return  to  its  primeval  home  ?  If  so,  had  we 
not  better  recast  our  definitions  of  matter  and  force ;  for  if  life  and 
thought  be  the  very  flower  of  both,  any  definition  which  omits  life  and 
thought  must  be  inadequate,  if  not  untrue.  Are  questions  like  these 
warranted  ?  Why  not  ?  If  the  final  goal  of  man  has  not  been  yet 
attained  ;  if  his  development  has  not  been  yet  arrested,  who  can  say  that 
such  yearnings  and  questionings  are  not  necessary  to  the  opening  of  a 
finer  vision,  to  the  budding  and  the  growth  of  diviner  powers  ?  When  I 
look  at  the  heavens  and  the  earth,  at  my  own  body,  at  my  strength  and 
weakness  of  mind,  even  at  these  ponderings,  and  ask  myself,  is  there  no 
being  or  thing  in  the  universe  that  knows  more  about  these  matters  than 
I  do ;  what  is  my  answer  ?  Supposing  our  theologic  schemes  of  crea- 
tion, condemnation,  and  redemption,  to  be  dissipated ;  and  the  warmth 
of  denial  which  they  excite,  and  which,  as  a  motive  force,  can  match  the 
warmth  of  affirmation  dissipated  at  the  same  time ;  would  the  undeflected 
human  mind  return  to  the  meridian  of  absolute  neutrality  as  regards  these 
ultra-physical  questions  ?  Is  such  a  position  one  of  stable  equilibrium  ? 
The  channels  of  thought  being  already  formed,  such  are  the  questions 
without  replies,  which  could  run  athwart  consciousness  during  a  ten- 
rninutes,  halt  upon  the  weathered  point  of  the  Matterhorn." 


VII. 

ON  THE 

SCIENTIFIC   USE  OF  THE  IMAGINATION, 

A  DISCOUKSE. 

DELIVERED  BEFORE  THE  BRITISH  ASSOCIATION  AT  LITERPOOL. 

September  16,  1870. 


"  If  thou  wouldst  know  the  mystic  song 
Chanted  when  the  sphere  was  young, 
Aloft,  abroad,  the  paean  swells, 
0  wise  man,  hear'st  thou  half  it  tells  ? 
To  the  open  ear  it  sings 
The  early  genesis  of  things ; 
Of  tendency  through  endless  ages 
Of  star-dust  and  star-pilgrimages, 
Of  rounded  worlds,  of  space  and  time, 
Of  the  old  floods'  subsiding  slime, 
Of  chemic  matter,  force  and  form, 
Of  poles  and  powers,  cold,  wet,  and  warm. 
The  rushing  metamorphosis 
Dissolving  all  that  fixture  is, 
Melts  things  that  be  to  things  that  seem, 
And  solid  Nature  to  a  dream." 

EMERSON. 


"  Was  war'  ein  Gott  der  nur  von  aussen  stiesse 
Im  Kreis  das  All  am  Finger  laufen  Hesse ! 
Ihm  ziemt's,  die  Welt  im  Innern  zu  bewegen, 
Natur  in  Sich,  Sich  in  Natur  zu  hegen." 

GOETHE. 


SCIENTIFIC   USE  OF  THE  IMAGINATION. 

"  Lastly,  physical  investigation  more  than  any  thing  besides  helps  to  teach 
us  the  actual  value  and  rigid  use  of  the  Imagination — of  that  wondrous 
faculty,  which,  left  to  ramble  uncontrolled,  leads  us  astray  into  a  wilderness  of 
perplexities  and  errors,  a  land  of  mists  and  shadows  ;  but  which  properly  con- 
trolled by  experience  and  reflection,  becomes  the  noblest  attribute  of  man :  the 
source  of  poetic  genius,  the  instrument  of  discovery  in  Science,  without  tlie  aid 
of  which  Newton  would  never  have  invented  jluxions,  nor  Davy  have  decom- 
posed the  earths  and  alkalies,  nor  would  Columbus  have  found  another  Con- 
tinent."— Address  to  the  Royal  Society  by  its  President,  Sir  Benjamin 
Brodie,  November  30,  1859. 

I  CARRIED  with  me  to  the  Alps  this  year  the  heavy 
burden  of  this  evening's  work.  In  the  way  of  new  inves- 
tigation I  had  nothing  complete  enough  to  be  brought 
before  you ;  so  all  that  remained  to  me  was  to  fall  back 
upon  such  residues  as  I  could  find  in  the  depths  of  con- 
sciousness, and  out  of  them  to  spin  the  fibre  and  weave  the 
web  of  this  discourse.  Save  from  memory  I  had  no  direct 
aid  upon  the  mountains ;  but  to  spur  up  the  emotions,  on 
which  so  much  depends,  as  well  as  to  nourish  indirectly  the 
intellect  and  will,  I  took  with  me  two  volumes  of  poetry, 
Goethe's  "  Farbenlehre,"  and  the  work  on  "  Logic  "  recently 
published  by  Mr.  Alexander  Bain.1  The  spur,  I  am  sorry 
to  say,  was  no  match  for  the  integument  of  dulness  it  had 

1  One  of  my  critics  remarks,  that  he  does  not  see  the  wit  of  calling 
Goethe's  "  Farbenlehre"  and  Bain's  "  Logic,"  "  two  volumes  of  poetry." 
Nor  do  I. 


128  FRAGMENTS  OF  SCIENCE. 

to  pierce.  In  Goethe,  so  glorious  otherwise,  I  chiefly 
noticed  the  self-inflicted  hurts  of  genius,  as  it  broke  itself 
in  vain  against  the  philosophy  of  Newton.  For  a  time, 
Mr.  Bain  became  my  principal  companion.  I  found  him 
learned  and  practical,  shining  generally  with  a  dry  light, 
but  exhibiting  at  times  a  flush  of  emotional  strength,  which 
proved  that  even  logicians  share  the  common  fire  of  hu- 
manity. He  interested  me  most  when  he  became  the 
mirror  of  my  own  condition.  Neither  intellectually  nor 
socially  is  it  good  for  man  to  be  alone,  and  the  griefs  of 
thought  are  more  patiently  borne  when  we  find  that  they 
have  been  experienced  by  another.  From  certain  passages 
in  his  book  I  could  infer  that  Mr.  Bain  was  no  stranger  to 
such  sorrows.  Take  this  passage  as  an  illustration.  Speak- 
ing of  the  ebb  of  intellectual  force,  which  we  all  from  time 
to  time  experience,  Mr.  Bain  says,  "  The  uncertainty  where 
to  look  for  the  next  opening  of  discovery  brings  the  pain  of 
conflict  and  the  debility  of  indecision."  These  words  have 
in  them  the  true  ring  of  personal  experience.  The  action 
of  the  investigator  is  periodic.  He  grapples  with  a  subject 
of  inquiry,  wrestles  with  it,  overcomes  it,  exhausts,  it  may 
be,  both  himself  and  it  for  the  time  being.  He  breathes  a 
space,  and  then  renews  the  struggle  in  another  field.  Now 
this  period  of  halting  between  two  investigations  is  not 
always  one  of  pure  repose.  It  is  often  a  period  of  doubt 
and  discomfort,  of  gloom  and  ennui.  "The  uncertainty 
where  to  look  for  the  next  opening  of  discovery  brings  the 
pain  of  conflict  and  the  debility  of  indecision."  Such  was 
my  precise  condition  in  the  Alps  this  year ;  in  a  score  of 
words  Mr.  Bain  has  here  sketched  my  mental  diagnosis ; 
and  it  was  under  these  evil  circumstances  that  I  had  to 
equip  myself  for  the  hour  and  the  ordeal  that  are  now 
come. 

/     Gladly,  however,  as  I  should  have  seen  this   duty  in 
other  hands,  I  could  by  no  means  shrink  from  it.     Disloy- 


SCIENTIFIC   USE  OF  THE  IMAGINATION.  129 

alty  would  have  been  worse  than  failure.  In  some  fashion 
or  other — feebly  or  strongly,  meanly  or  manfully,  on  the 
higher  levels  of  thought,  or  on  the  flats  of  commonplace — 
the  task  had  to  be  accomplished.  I  looked  in  various  direc- 
tions for  help  and  furtherance ;  but  without  me  for  a  time 
I  saw  only  "  antres  vast,"  and  within  me  "deserts  idle." 
>My  case  resembled  that  of  a  sick  doctor  who  had  forgotten 
his  art  and  sorely  needed  the  prescription  of  a  friend.  Mr. 
Bain  wrote  one  for  me.  He  said,  "  Your  present  knowl- 
edge must  forge  the  links  of  connection  between  what  has 
been  already  achieved  and  what  is  now  required."  3  In 
these  words  he  admonished  me  to  review  the  past  and  re- 
cover from  it  the  broken  ends  of  former  investigations.  I 
tried  to  do  so.  Previous  to  going  to  Switzerland  I  had 
been  thinking  much  of  light  and  heat,  of  magnetism  and 
electricity,  of  organic  germs,  atoms,  molecules,  spontaneous 
generation,  comets,  and  skies.  With  one  or  another  of 
these  I  now  sought  to  reform  an  alliance,  and  finally  suc- 
ceeded in  establishing  a  kind  of  cohesion  between  Thought 
and  Light.  The  wish  grew  within  me  to  trace,  and  to  en- 
able you  to  trace,  some  of  the  more  occult  operations  of 
this  agent.  I  wished,  if  possible,  to  take  you  behind  the 
drop-scene  of  the  senses,  and  to  show  you  the  hidden  mech- 
anism of  optical  action.  For  I  take  it  to  be  well  worth 
the  while  of  the  scientific  teacher  to  take  some  pains,  and 
even  great  pains,  to  make  those  whom  he  addresses  copart- 
ners of  his  thoughts.  To  clear  his  own  mind  in  the  first  place 
of  all  haze  and  vagueness,  and  then  to  project  into  lan- 
guage which  shall  leave  no  mistake  as  to  his  meaning — 
which  shall  leave  even  his  errors  naked — the  definite  ideas 
he  has  shaped.  A  great  deal  is,  I  think,  possible  to  scien- 
tific exposition  conducted  in  this  way.  It  is  possible,  I 
believe,  even  before  an  audience  like  the  present,  to  un- 
cover to  some  extent  the  unseen  things  of  Nature;  and 

1  Induction,  p.  422. 


130  FRAGMENTS  OF  SCIENCE. 

thus  to  give  not  only  to  professed  students,  but  to  others 
with  the  necessary  bias,  industry,  and  capacity,  an  intelli- 
gent interest  in  the  operations  of  science.  Time  and  labor 
are  necessary  to  this  result,  but  science  is  the  gainer  from 
the  public  sympathy  thus  created. 

How,  then,  are  those  hidden  things  to  be  revealed  ? 
How,  for  example,  are  we  to  lay  hold  of  the  physical  basis 
of  light,  since,  like  that  of  life  itself,  it  lies  entirely  without 
the  domain  of  the  senses  ?  Philosophers  may  be  right  in 
affirming  that  we  cannot  transcend  experience ;  but  we  can 
at  all  events  carry  it  a  long  way  from  its  origin.  We  can  also 
magnify,  diminish,  qualify,  and  combine  experiences,  so  as  to 
render  them  fit  for  purposes  entirely  new.  We  are  gifted 
with  the  power  of  imagination — combining  what  the  Ger- 
mans call  Anschauungsgabe  and  Einbildungskraft — and  by 
this  power  we  can  lighten  the  darkness  which  surrounds  the 
world  of  the  senses.  There  are  tories  even  in  science  who 
regard  imagination  as  a  faculty  to  be  feared  and  avoided 
rather  than  employed.  They  had  observed  its  action  in 
weak  vessels,  and  were  unduly  impressed  by  its  disasters. 
But  they  might  with  equal  justice  point  to  exploded  boil- 
ers as  an  argument  against  the  use  of  steam.  Bounded  and 
conditioned  by  cooperant  Reason,  imagination  becomes  the 
mightiest  instrument  of  the  physical  discoverer.  Newton's 
passage  from  a  falling  apple  to  a  falling  moon  was,  at  the 
outset,  a  leap  of  the  imagination.  When  William  Thom- 
son tries  to  place  the  ultimate  particles  of  matter  between 
his  compass-points,  and  to  apply  to  them  a  scale  of  milli- 
metres, he  is  powerfully  aided  by  this  faculty.  And  in 
much  that  has  been  recently  said  about  protoplasm  and 
life,  we  have  the  outgoings  of  the  imagination  guided  and 
controlled  by  the  known  analogies  of  science.  In  fact, 
without  this  power,  our  knowledge  of  Nature  would  be  a 
mere  tabulation  of  coexistences  and  sequences.  We  should 
still  believe  in  the  succession  of  day  and  night,  of  summer 


SCIENTIFIC  USE   OF  THE  IMAGINATION.  131 

and  winter ;  but  the  soul  of  Force  would  be  dislodged  from 
our  universe ;  causal  relations  would  disappear,  and  with 
them  that  science  which  is  now  binding  the  parts  of  Nature 
to  an  organic  whole. 

/  I  should  like  to  illustrate  by  a  few  simple  instances  the 
use  that  scientific  men  have  already  made  of  this  power  of 
imagination,  and  to  indicate  afterward  some  of  the  further 
uses  that  they  are  likely  to  make  of  it.  Let  us  begin  with 
the  rudimentary  experiences.  Observe  the  falling  of  heavy 
rain-drops  into  a  tranquil  pond.  Each  drop  as  it  strikes  the 
water  becomes  a  centre  of  disturbance,  from  which  a  series 
of  ring-ripples  expand  outwards.  Gravity  and  inertia  are 
the  agents  by  which  this  wave-motion  is  produced,  and  a 
rough  experiment  will  suffice  to  show  that  the  rate  of 
propagation  does  not  amount  to  a  foot  a  second.  A  series 
of  slight  mechanical  shocks  is  experienced  by  a  body 
plunged  in  the  water  as  the  wavelets  reach  it  in  succes- 
sion. But  a  finer  motion  is  at  the  same  time  set  up  and 
propagated.  If  the  head  and  ears  be  immersed  in  the  wa- 
ter, as  in  an  experiment  of  Franklin's,  the  shock  of  the 
drop  is  communicated  to  the  auditory  nerve — the  tick  of 
the  drop  is  heard.  Now  this  sonorous  impulse  is  propa- 
gated, not  at  the  rate  of  a  foot  a  second,  but  at  the  rate  of 
forty-seven  hundred  feet  a  second.  In  this  case  it  is  not 
the  gravity,  but  the  elasticity  of  the  water  that  is  the  ur- 
ging force.  Every  liquid  particle  pushed  against  its  neigh- 
bor delivers  up  its  motion  with  extreme  rapidity,  and  the 
pulse  is  propagated  as  a  thrill.  The  incompressibility  of 
water,  as  illustrated  by  the  famous  Florentine  experiment, 
is  a  measure  of  its  elasticity,  and  to  the  possession  of  this 
property  in  so  high  a  degree  the  rapid  transmission  of  a 
sound-pulse  through  water  is  to  be  ascribed. 

But  water,  as  youiknow,  is  not  necessary  to  the  conduc- 
tion of  sound ;  air  is  its  most  common  vehicle.  And  you 
know  that  when  the  air  possesses  the  particular  density 


132  FRAGMENTS  OF  SCIENCE. 

and  elasticity  corresponding  to  the  temperature  of  freezing- 
water  the  velocity  of  sound  in  it  is  ten  hundred  and  ninety 
feet  a  second.  It  is  almost  exactly  one-fourth  of  the  ve- 
locity in  water ;  the  reason  being  that  though  the  greater 
weight  of  the  water  tends  to  diminish  the  velocity,  the 
enormous  molecular  elasticity  of  the  liquid  far  more  than 
atones  for  the  disadvantage  due  to  weight.  By  various 
contrivances  we  can  compel  the  vibrations  of  the  air  to 
declare  themselves ;  we  know  the  length  and  frequency  of 
sonorous  waves,  and  we  have  also  obtained  great  mastery 
over  the  various  methods  by  which  the  air  is  thrown  into 
vibration.  We  know  the  phenomena  and  laws  of  vibrating 
rods,  of  organ-pipes,  strings,  membranes,  plates,  and  bells. 
We  can  abolish  one  sound  by  another.  We  know  the 
physical  meaning  of  music  and  noise,  of  harmony  and  dis- 
cord. In  short,  as  regards  sounds  we  have  a  very  clear 
notion  of  the  external  physical  processes  which  corre- 
spond to  our  sensations. 

In  these  phenomena  of  sound  we  travel  a  very  little 
way  from  downright  sensible  experience.  Still  the  imagi- 
nation is  to  some  extent  exercised.  The  bodily  eye,  for 
example,  cannot  see  the  condensations  and  rarefactions  of 
the  waves  of  sound.  We  construct  them  in  thought,  and 
we  believe  as  firmly  in  their  existence  as  in  that  of  the  air 
itself.  But  now  our  experience  has  to  be  carried  into  a 
new  region,  where  a  new  use  is  to  be  made  of  it.  Having 
mastered  the  cause  and  mechanism  of  sound,  we  desire  to 
know  the  cause  and  mechanism  of  light.  We  wish  to  ex- 
tend our  inquiries  from  the  auditory  nerve  to  the  optic  nerve. 
There  is  in  the  human  intellect  a  power  of  expansion^— I 
might  almost  call  it  a  power  of  creation^-which  is  brought 
into  play  by  the  simple  brooding  upon  facts.  The  legend 
of  the  Spirit  brooding  over  chaos  may  have  originated  in  a 
knowledge  of  this  power.  In  the  case  now  before  us  it  has 
manifested  itself  by  transplanting  into  space,  for  the  pur- 


SCIENTIFIC  USE   OF  THE  IMAGINATION.  133 

poses  of  light,  an  adequately  modified  form  of  the  mechan- 
ism of  sound.  We  know  intimately  whereon  the  velocity 
of  sound  depends.  When  we  lessen  the  density  of  a  medium 
and  preserve  its  elasticity  constant  we  augment  the  velocity. 
When  we  heighten  the  elasticity  and  keep  the  density  con- 
stant we  also  augment  the  velocity.  A  small  density, 
therefore,  and  a  great  elasticity,  are  the  two  things  neces- 
sary to  rapid  propagation.  Now  light  is  known  to  move 
with  the  astounding  velocity  of  185,000  miles  a  second. 
How  is  such  a  velocity  to  be  obtained?  By  boldly  dif- 
fusing in  space  a  medium  of  the  requisite  tenuity  and 
elasticity. 

Let  us  make  such  a  medium  our  starting-point,  endow- 
ing it  with  one  or  two  other  necessary  qualities ;  let  us 
handle  it  in  accordance  with  strict  mechanical  laws  ;  let  us 
give  to  every  step  of  our  deduction  the  surety  of  the  syl- 
logism ;  let  us  carry  it  thus  forth  from  the  world  of  imagi- 
nation into  the  world  of  sense,  and  see  whether  the  final 
outcrop  of  the  deduction  be  not  the  very  phenomena  of 
light  which  ordinary  knowledge  and  skilled  experiment  re- 
veal. If  in  all  the  multiplied  varieties  of  these  phenomena, 
including  those  of  the  most  remote  and  entangled  descrip- 
tion, this  fundamental  conception  always  brings  us  face  to 
face  with  the  truth ;  if  no  contradiction  to  our  deductions 
from  it  be  found  in  external  Nature,  but  on  all  sides  agree- 
ment and  verification  ;  if,  moreover,  as  in  the  case  of  Coni- 
cal Refraction  and  in  other  cases,  it  has  actually  forced 
upon  our  attention  phenomena  which  no  eye  had  previously 
seen,  and  which  no  mind  had  previously  imagined,  such  a 
conception,  which  never  disappoints  us,  but  always  lands 
us  on  the  solid  shores  of  fact,  must,  we  think,  be  something 
more  than  a  mere  figment  of  the  scientific  fancy.  In  form- 
ing it  that  composite  and  creative  unity  in  which  reason 
and  imagination  are  together  blent,  has,  we  believe,  led  us 
into  a  world  not  less  real  than  that  of  the  senses,  and  of 


134  FRAGMENTS  OF  SCIENCE. 

which  the  world  of  sense  itself  is  the  suggestion  and  justi- 
fication. 

Far  be  it  from  me,  however,  to  wish  to  fix  you  immov- 
ably in  this  or  in  any  other  theoretic  conception.  With 
all  our  belief  of  it,  it  will  be  well  to  keep  the  theory  plastic 
and  capable  of  change.  You  may,  moreover,  urge  that 
although  the  phenomena  occur  as  if  the  medium  existed, 
the  absolute  demonstration  of  its  existence  is  still  wanting. 
Far  be  it  from  me  to  deny  to  this  reasoning  such  validity 
as  it  may  fairly  claim.  Let  us  endeavor  by  means  of  anal- 
ogy to  form  a  fair  estimate  of  its  force.  You  believe  that 
in  society  you  are  surrounded  by  reasonable  beings  like 
yourself.  You  are  perhaps  as  firmly  convinced  of  this  as 
of  any  thing.  What  is  your  warrant  for  this  conviction  ? 
Simply  and  solely  this,  your  fellow-creatures  behave  as  if 
they  were  reasonable ;  the  hypothesis,  for  it  is  nothing 
more,  accounts  for  the  facts.  To  take  an  eminent  example : 
you  believe  that  our  President  is  a  reasonable  being.  Why  ? 
There  is  no  known  method  of  superposition  by  which  any 
one  of  us  can  apply  himself  intellectually  to  another  so  as 
to  demonstrate  coincidence  as  regards  the  possession  of 
reason.  If,  therefore,  you  hold  our  President  to  be  reason- 
able, it  is  because  he  behaves  as  if  he  were  reasonable.  As 
in  the  case  of  the  ether,  beyond  the  "  as  if"  you  cannot  go. 
Nay  I  should  not  wonder  if  a  close  comparison  of  the  data 
on  which  both  inferences  rest,  caused  many  respectable 
persons  to  conclude  that  the  ether  had  the  best  of  it. 

This  universal  medium,  this  light-ether  as  it  is  called,  is 
a  vehicle,  not  an  origin  of  wave-motion.  It  receives  and 
transmits,  but  it  does  not  create.  Whence  does  it  derive 
the  motions  it  conveys  ?  For  the  most  part  from  luminous 
bodies.  By  this  motion  of  a  luminous  body  I  do  not  mean 
its  sensible  motion,  such  as  the  flicker  of  a  candle,  or  the 
shooting  out  of  red  prominences  from  the  limb  of  the  sun. 
I  mean  an  intestine  motion  of  the  atoms  or  molecules  of 


SCIENTIFIC   USE   OF   THE   IMAGINATION.  135 

the  luminous  body.  But  here  a  certain  reserve  is  necessary. 
Many  chemists  of  the  present  day  refuse  to  speak  of  atoms 
and  molecules  as  real  things.  Their  caution  leads  them  to 
stop  short  of  the  clear,  sharp,  mechanically  intelligible 
atomic  theory  enunciated  by  Dalton,  or  any  form  of  that 
theory,  and  to  make  the  doctrine  of  multiple  proportions 
their  intellectual  bourne.  I  respect  the  caution,  though  I 
think  it  is  here  misplaced.  The  chemists  who  recoil  from 
these  notions  of  atoms  and  molecules  accept  without  hesita- 
tion the  Undulatory  Theory  of  Light.  Like  you  and  me, 
they  one  and  all  believe  in  an  ether  and  its  light-producing 
waves.  Let  us  consider  what  this  belief  involves.  Bring 
your  imaginations  once  more  into  play  and  figure  a  series 
of  sound-waves  passing  through  air.  Follow  them  up  to 
their  origin,  and  what  do  you  there  find  ?  A  definite,  tan- 
gible, vibrating  body.  It  may  be  the  vocal  chords  of  a 
human  being,  it  may  be  an  organ-pipe,  or  it  may  be  a 
stretched  string.  Follow  in  the  same  manner  a  train  of 
ether-waves  to  their  source ;  remembering  at  the  same  time 
that  your  ether  is  matter,  dense,  elastic,  and  capable  of 
motions  subject  to  and  determined  by  mechanical  laws. 
What  then  do  you  expect  to  find  as  the  source  of  a  series 
of  ether-waves  ?  Ask  your  imagination  if  it  will  accept  a 
vibrating  multiple  proportion — a  numerical  ratio  in  a  state 
of  oscillation  ?  I  do  not  think  it  will.  You  cannot  crown 
the  edifice  by  this  abstraction.  The  scientific  imagination, 
which  is  here  authoritative,  demands  as  the  origin  and  cause 
of  a  series  of  ether-waves  a  particle  of  vibrating  matter 
quite  as  definite,  though  it  may  be  excessively  minute,  as 
that  which  gives  origin  to  a  musical  sound.  Such  a  particle 
we  name  an  atom  or  a  molecule.  I  think  the  seeking  intel- 
lect when  focussed  so  as  to  give  definition  without  penum- 
bral  haze,  is  sure  to  realize  this  image  at  the  last. 

With  a  view  of  preserving  thought  continuous  through- 
out this  discourse,  and  of  preventing  either  failure  of  knowl- 


136  FRAGMENTS  OF  SCIENCE. 

edge  or  of  memory  from  causing  any  rent  in  our  picture,  I 
here  propose  to  run  rapidly  over  a  bit  of  ground  which  is 
probably  familiar  to  most  of  you,  but  which  I  am  anxious  to 
make  familiar  to  you  all.  The  waves  generated  in  the  ether 
by  the  swinging  atoms  of  luminous  bodies  are  of  different 
lengths  and  amplitudes.  The  amplitude  is  the  width  of 
swing  of  the  individual  particles  of  the  wave.  In  water- 
waves  it  is  the  height  of  the  crest  above  the  trough,  while 
the  length  of  the  wave  is  the  distance  between  two  con- 
secutive crests.  The  aggregate  of  waves  emitted  by  the  sun 
may  be  broadly  divided  into  two  classes :  the  one  class  com- 
petent, the  other  incompetent,  to  excite  vision.  But  the 
light-producing  waves  differ  markedly  among  themselves 
in  size,  form,  and  force.  The  length  of  the  largest  of  these 
waves  is  about  twice  that  of  the  smallest,  but  the  amplitude 
of  the  largest  is  probably  a  hundred  times  that  of  the 
smallest.  Now  the  force  or  energy  of  the  wave,  which,  ex- 
pressed with  reference  to  sensation,  means  the  intensity  of 
the  light,  is  proportional  to  the  square  of  the  amplitude. 
Hence  the  amplitude  being  one-hundred-fold,  the  energy  of 
the  largest  light-giving  waves  would  be  ten-thousand-fold 
that  of  the  smallest.  This  is  not  improbable.  I  use  these 
figures  not  with  a  view  to  numerical  accuracy,  but  to  give 
you  definite  ideas  of  the  differences  that  probably  exist 
among  the  light-giving  waves.  And  if  we  take  the  whole 
range  of  solar  radiation  into  account — its  non-visual  as  well 
as  its,  visual  waves — I  think  it  probable  that  the  force  or 
eo^fgy  of  the  largest  wave  is  a  million  times  that  of  the 
smallest. 

Turned  into  their  equivalents  of  sensation,  the  different 
light-waves  produce  different  colors.  Red,  for  example,  is 
roduced  by  the  largest  waves,  violet  by  the  smallest,  while 
green  is  produced  by  a  wave  of  intermediate  length  and 
amplitude.  On  entering  from  air  into  more  highly  refract- 
ing substances,  such  as  glass  or  water,  or  the  sulphide  of 


SCIENTIFIC  USE  OF  THE  IMAGINATION.  137 

carbon,  all  the  waves  are  retarded,  but  the  smallest  ones 
most.  This  furnishes  a  means  of  separating  the  different 
classes  of  waves  from  each  other ;  in  other  words,  of  ana- 
lyzing the  light.  Sent  through  a  refracting  prism,  the  waves 
of  the  sun  are  turned  aside  in  different  degrees  from  their 
direct  course,  the  red  least,  the  violet  most.  They  are  vir- 
tually pulled  asunder,  and  they  paint  upon  a  white  screen 
placed  to  receive  them  "the  solar  spectrum."  Strictly 
speaking,  the  spectrum  embraces  an  infinity  of  colors,  but 
the  limits  of  language  and  of  our  powers  of  distinction  cause 
it  to  be  divided  into  seven  segments :  red,  orange,  yellow, 
green,  blue,  indigo,  violet.  These  are  the  seven  primary  or 
prismatic  colors. 

Separately,  or  mixed  in, various  proportions,  the  solar 
waves  yield  all  the  colors  observed  in  nature  and  employed 
in  art.  Collectively,  they  give  us  the  impression  of  white- 
ness. Pure  unsifted  solar  light  is  white ;  and  if  all  the 
wave-constituents  of  such  light  be  reduced  in  the  same  pro- 
portion the  light,  though  diminished  in  intensity,  will  still 
be  white.  The  whiteness  of  Alpine  snow  with  the  sun 
shining  upon  it,  is  barely  tolerable  to  the  eye.  The  same 
snow  under  an  overcast  firmament  is  still  white.  Such  a 
firmament  enfeebles  the  light  by  reflection,  and  when  we  lift 
ourselves  above  a  cloud-field — to  an  Alpine  summit,  for  in- 
stance, or  to  the  top  of  Snowdon — and  see,  in  the  proper 
direction,  the  sun  shining  on  the  clouds,  they  appear  daz- 
zlingly  white.  Ordinary  clouds,  in  fact,  divide  the  solar 
light  impinging  on  them  into  two  parts — a  reflected  part 
and  a  transmitted  part,  in  each  of  which  the  proportions  of 
wave-motion  which  produce  the  impression  of  whiteness 
are  sensibly  preserved. 

It  will  be  understood  that  the  conditions  of  whiteness 
would  fail  if  all  the  waves  were  diminished  equally r,  or  by 
the  same  absolute  quantity.  They  must  be  reduced  pro- 
portionately, instead  of  equally.  If  by  the  act  of  reflection 


138  FRAGMENTS  OF  SCIENCE. 

the  waves  of  red  light  are  split  into  exact  halves,  then,  to 
preserve  the  light  white,  the  waves  of  yellow,  orange,  green, 
and  blue  must  also  be  split  into  exact  halves.  In  short,  the 
reduction  must  take  place,  not  by  absolutely  equal  quanti- 
ties, but  by  equal  fractional  parts.  In  white  light  the  pre- 
ponderance as  regards  energy  of  the  latter  over  the  smaller 
waves  must  always  be  immense.  Were  the  case  otherwise, 
the  physiological  correlative,  blue,  of  the  smaller  waves 
would  have  the  upper  hand  in  our  sensations. 

My  wish  to  render  our  mental  images  complete,  causes 
me  to  dwell  briefly  upon  these  known  points,  and  the 
same  wish  will  cause  me  to  linger  a  little  longer  among 
others.  But  here  I  am  disturbed  by  my  reflections.  When 
/I  consider  the  effect  of  dinner  upon  the  nervous  system,  and 
the  relation  of  that  system  to  the  intellectual  powers  I  am 
now  invoking — when  I  remember  that  the  universal  expe- 
rience of  mankind  has  fixed  upon  certain  definite  elements 
of  perfection  in  an  after-dinner  speech,  and  when  I  think 
how  conspicuous  by  their  absence  these  elements  are  on  the 
present  occasion,  the  thought  is  not  comforting  to  a  man 
who  wishes  to  stand  well  with  his  fellow-creatures  in  gen- 
eral, and  with  the  members  of  the  British  Association  in 
particular.  My  condition  might  well  resemble  that  of  the 
ether,  which  is  scientifically  defined  as  an  assemblage  of 
vibrations.  And  the  worst  of  it  is,  that  unless  you  reverse 
the  general  verdict  regarding  the  effect  of  dinner,  and  prove 
in  your  own  persons  that  a  uniform  experience  need  not  con- 
tinue uniform — which  will  be  a  great  point  gained  for  some 
people — these  tremors  of  mine  are  likely  to  become  more 
and  more  painful.  But  I  call  to  m  jpd  the  comforting  words 
of  an  inspired  though  uncanonical  writer,  who  admonishes 
us  in  the  Apocrypha  that  fear  is  a  bad  counsellor.  Let  me 
then  cast  him  out,  and  let  me  trustfully  assume  that  you 
will  one  and  all  postpone  that  balmy  sleep,  of  which  dinner, 
might  under  the  circumstances  be  regarded  as  the  indis- 


SCIENTIFIC  USE  OF  THE  IMAGINATION.  139 

soluble  antecedent,  and  that  you  will  manfully  and  woman- 
fully  prolong  your  investigations  of  the  ether  and  its  waves 
into  regions  which  have  been  hitherto  crossed  by  the 
pioneers  of  science  alone. 

Not  only  are  the  waves  of  ether  reflected  by  clouds, 
by  solids,  and  by  liquids,  but  when  they  pass  from  light  air 
to  dense,  or  from  dense  air  to  light,  a  portion  of  the  wave- 
motion  is  always  reflected.  Now  our  atmosphere  changes 
continually  in  density  from  top  to  bottom.  It  will  help 
our  conceptions  if  we  regard  it  as  made  up  of  a  series  of  thin 
concentric  layers,  or  shells  of  air,  each  shell  being  of  the 
same  density  throughout,  and  a  small  and  sudden  change 
of  density  occurring  in  passing  from  shell  to  shell.  Light 
would  be  reflected  at  the  limiting  surfaces  of  all  these  shells, 
and  their  action  would  be  practically  the  same  as  that  of  the 
real  atmosphere.  And  now  I  would  ask  your  imagination 
to  picture  this  act  of  reflection.  What  must  become  of  the 
reflected  light  ?  The  atmospheric  layers  turn  their  convex 
surfaces  toward  the  sun  ;  they  are  so  many  convex  mirrors 
of  feeble  power,  and  you  will  immediately  perceive  fhat  the 
light  regularly  reflected  from  these  surfaces  cannot  reach 
the  earth  at  all,  but  is  dispersed  in  space. 

But  though  the  sun's  light  is  not  reflected  in  this  fashion 
from  the  aerial  layers  to  the  earth,  there  is  indubitable  evi- 
dence to  show  that  the  light  of  our  firmament  is  reflected 
light.  Proofs  of  the  most  cogent  description  could  be  here 
adduced  ;  but  we  need  only  consider  that  we  receive  light 
at  the  same  time  from  all  parts  of  the  hemisphere  of  heav- 
en. The  light  of  the  firmament  comes  to  us  across  the  di- 
rection of  the  solar  rays,  and  even  against  the  direction  of 
the  solar  rays  ;  and  this  lateral  and  opposing  rush  of  wave- 
motion  can  only  be  due  to  the  rebound  of  the  waves  from 
the  air  itself,  or  from  something  suspended  in  the  air.  It  is 
also  evident  that,  unlike  the  action  of  clouds,  the  solar  light 
is  not  reflected  by  the  sky  in  the  proportions  which  produce 


140  FRAGMENTS  OF  SCIENCE. 

white.  The  sky  is  blue,  which  indicates  a  deficiency  on  part 
of  the  larger  waves.  In  accounting  for  the  color  of  the  sky, 
the  first  question  suggested  by  the  analogy  would  undoubt- 
edly be,  Is  not  the  air  blue  ?  The  blueness  of  the  air  has 
in  fact  been  given  as  a  solution  of  the  blueness  of  the  sky. 
But  reason,  basing  itself  on  observation,  asks  in  reply,  How, 
if  the  air  be  blue,  can  the  light  of  sunrise  and  sunset,  which 
travels  through  vast  distances  of  air,  be  yellow,  orange,  or 
even  red  ?  The  passage  of  white  solar  light  through  a  blue 
medium  could  by  no  possibility  redden  the  light.  The  hy- 
pothesis of  a  blue  air  is  therefore  untenable.  In  fact,  the 
agent,  whatever  it  is,  which  sends  us  the  light  of  the  sky, 
exercises  in  so  doing  a  dichroitic  action.  The  light  reflected 
is  blue,  the  light  transmitted  is  orange  or  red.  A  marked 
distinction  is  thus  exhibited  between  the  matter  of  the  sky 
and  that  of  an  ordinary  cloud,  which  exercises  no  such  di- 
chroitic action. 

By  the  force  of  imagination  and  reason  combined  we 
may  penetrate  this  mystery  also.  The  cloud  takes  no  note 
of  size  on  the  part  of  the  waves  of  ether,  but  reflects  them 
ah1  alike.  It  exercises  no  selective  action.  Now,  the  cause 
of  this  may  be  that  the  cloud-particles  are  so  large  in  com- 
parison with  the  size  of  the  waves  of  ether  as  to  reflect  them 
all  indifferently.  A  broad  cliff  reflects  an  Atlantic  roller  as 
easily  as  a  ripple  produced  by  a  sea-bird's  wing ;  and  in  the 
presence  of  large  reflecting  surfaces,  the  existing  differences 
of  magnitude  among  the  waves  of  ether  may  disappear. 
But  supposing  the  reflecting  particles,  instead  of  being  very 
large,  to  be  very  small,  in  comparison  with  the  size  of  the 
waves.  In  this  case,  instead  of  the  whole  wave  being 
fronted  and  in  great  part  thrown  back,  a  small  portion  only 
is  shivered  off.  The  great  mass  of  the  wave  passes  over 
such  a  particle  without  reflection.  Scatter,  then,  a  handful 
of  such  minute  foreign  particles  in  our  atmosphere,  and  set 
imagination  to  watch  their  action  upon  the  solar  waves. 


SCIENTIFIC  USE   OF  THE  IMAGINATION.  141 

Waves  of  all  sizes  impinge  upon  the  particles,  and  you  see 
at  every  collision  a  portion  of  the  impinging  wave  struck 
off.  All  the  waves  of  the  spectrum,  from  the  extreme  red 
to  the  extreme  violet,  are  thus  acted  upon.  But  in  what 
proportions  will  the  waves  be  scattered  ?  A  clear  picture 
will  enable  us  to  anticipate  the  experimental  answer.  Re- 
membering that  the  red  waves  are  to  the  blue  much  in  the 
relation  of  billows  to  ripples,  let  us  consider  whether  those 
extremely  small  particles  are  competent  to  scatter  all  the 
waves  in  the  same  proportion.  If  they  be  not — and  a  little 
reflection  will  make  it  clear  to  you  that  they  are  not — the 
production  of  color  must  be  an  incident  of  the  scattering. 
Largeness  is  a  thing  of  relation  ;  and  the  smaller  the  wave, 
the  greater  is  the  relative  size  of  any  particle  on  which  the 
wave  impinges,  and  the  greater  also  the  ratio  of  the  scat- 
tered portion  to  the  total  wave.  A  pebble  placed  in  the 
way  of  the  ring-ripples  produced  by  our  heavy  rain-drops 
on  a  tranquil  pond  will  throw  back  a  large  fraction  of  the 
ripple  incident  upon  it,  while  the  fractional  part  of  a  larger 
wave  thrown  back  by  the  same  pebble  might  be  infinitesi- 
mal. -  Now  we  have  already  made  it  clear  to  our  minds 
that  to  preserve  the  solar  light  white,  its  constituent  pro- 
portions must  not  be  altered ;  but  in  the  act  of  division 
performed  by  these  very  small  particles  we  see  that  the 
proportions  are  altered ;  an  undue  fraction  of  the  smaller 
waves  is  scattered  by  the  particles,  and,  as  a  consequence, 
in  the  scattered  light,  blue  will  be  the  predominant  color. 
The  other  colors  of  the  spectrum  must,  to  some  extent,  be 
associated  with  the  blue.  They  are  not  absent  but  deficient. 
We  ought,  in  fact,  to  have  them  all,  but  in  diminishing  pro- 
portions, from  the  violet  to  the  red. 

We  have  here  presented  a  case  to  the  imagination,  and, 
assuming  the  undulatory  theory  to  be  a  reality,  we  have,  I 
think,  fairly  reasoned  our  way  to  the  conclusion  that,  were 
particles,  small  in  comparison  to  the  size  of  the  ether-waves. 


142  FRAGMENTS  OF  SCIENCE. 

sown  in  our  atmosphere,  the  light  scattered  by  those  parti- 
cles would  be  exactly  such  as  we  observe  in  our  azure  skies. 
When  this  light  is  analyzed,  all  the  colors  of  the  spectrum 
are  found ;  but  they  are  found  in  the  proportions  indicated 
by  our  conclusion. 

Let  us  now  turn  our  attention  to  the  light  which  passes 
unscattered  among  the  particles.  How  must  it  be  finally 
affected  ?  By  its  successive  collisions  with  the  particles, 
the  white  light  is  more  and  more  robbed  of  its  shorter 
waves  ;  it  therefore  loses  more  and  more  of  its  due  propor- 
tion of  blue.  The  result  may  be  anticipated.  The  trans- 
mitted light,  where  short  distances  are  involved,  will  appear 
yellowish.  But  as  the  sun  sinks  toward  the  horizon  the 
atmospheric  distances  increase,  and  consequently  the  num- 
ber of  the  scattering  particles.  They  abstract  in  succession 
the  violet,  the  indigo,  the  blue,  and  even  disturb  the  pro- 
portions of  green.  The  transmitted  light  under  such  cir- 
cumstances must  pass  from  yellow  through  orange  to  red. 
This  also  is  exactly  what  we  find  in  Nature.  Thus,  while 
the  reflected  light  gives  us  at  noon  the  deep  azure  of  the 
Alpine  skies,  the  transmitted  light  gives  us  at  sunset  the 
warm  crimson  of  the  Alpine  snows.  The  phenomena  cer- 
tainly occur  as  if  our  atmosphere  were  a  medium  rendered 
slightly  turbid  by  the  mechanical  suspension  of  exceedingly 
small  foreign  particles. 

Here,  as  before,  we  encounter  our  skeptical  "  as  if"  It 
is  one  of  the  parasites  of  science,  ever  at  hand,  and  ready 
to  plant  itself  and  sprout,  if  it  can,  on  the  weak  points  of 
our  philosophy.  But  a  strong  constitution  defies  the  para- 
site, and  in  our  case,  as  we  question  the  phenomena,  proba- 
bility grows  like  growing  health,  until  in  the  end  the  malady 
of  doubt  is  completely  extirpated.  The  first  question  that 
naturally  arises  is,  Can  small  particles  be  really  proved  to 
act  in  the  manner  indicated  ?  No  doubt  of  it.  Each  one 
of  you  can  submit  the  question  to  an  experimental  test. 


SCIENTIFIC  USE   OF   THE  IMAGINATION.  143 

Water  will  not  dissolve  resin,  but  spirit  will;  and  when 
spirit  which  holds  resin  in  solution  is  dropped  into  water, 
the  resin  immediately  separates  in  solid  particles,  which 
render  the  water  milky.  The  coarseness  of  this  precipitate 
depends  on  the  quantity  of  the  dissolved  resin.  You  can 
cause  it  to  separate  in  thick  clots  or  in  exceedingly  fine 
particles.  Professor  Brlicke  has  given  us  the  proportions 
which  produce  particles  particularly  suited  to  our  present 
purpose.  One  gramme  of  clean  mastic  is  dissolved  in 
eighty-seven  grammes  of  absolute  alcohol,  and  the  trans- 
parent solution  is  allowed  to  drop  into  a  beaker  containing 
clear  water  kept  briskly  stirred.  An  exceedingly  fine 
precipitate  is  thus  formed,  which  declares  its  presence  by 
its  action  upon  light.  Placing  a  dark  surface  behind  the 
beaker,  and  permitting  the  light  to  fall  into  it  from  the  top 
or  front,  the  medium  is  seen  to  be  distinctly  blue.  It  is  not 
perhaps  so  perfect  a  blue  as  I  have  seen  on  exceptional 
days,  this  year,  among  the  Alps,  but  it  is  a  very  fair  sky- 
blue.  A  trace  of  soap  in  water  gives  a  tint  of  blue.  Lon- 
/don,  and  I  fear  Liverpool  milk,  makes  an  approximation  to 
the  same  color  through  the  operation  of  the  same  cause ; 
and  Helmholtz  has  irreverently  disclosed  the  fact  that  the 
deepest  blue  eye  is  simply  a  turbid  medium. 

The  action  of  turbid  media  upon  light  was  illustrated 
by  Goethe,  who,  though  unacquainted  with  the  undula- 
tory  theory,  was  led  by  his  experiments  to  regard  the 
firmament  as  an  illuminated  turbid  medium  with  the  dark- 
ness of  space  behind  it.  He  describes  glasses  showing  a 
bright  yellow  by  transmitted,  and  a  beautiful  blue  by  re- 
flected light.  Professor  Stokes,  who  was  probably  the  first 
to  discern  the  real  nature  of  the  action  of  small  particles 
on  the  waves  of  ether,  describes  a  glass  of  a  similar  kind.1 

1  This  glass,  by  reflected  light,  had  a  color  "  strongly  resembling  that 
of  a  decoction  of  a  horse-chestnut  bark."  Curiously  enough,  Goethe 
refers  to  this  very  decoction :  "  Man  nehme  "einen  Streifcn  frischer  Rinde 


144  FRAGMENTS  OF  SCIENCE. 

Capital  specimens  of  such  glass  are  to  be  found  at  Salviati's 
in  St.  James's  Street.  What  artists  call  "chill"  is  no 
doubt  an  effect  of  this  description.  Through  the  action  of 
minute  particles,  the  browns  of  a  picture  often  present  the 
appearance  of  the  bloom  of  a  plum.  By  rubbing  the  var- 
nish with  a  silk  handkerchief  optical  continuity  is  estab- 
lished, and  the  chill  disappears.  Some  years  ago  I  wit- 
nessed Mr.  Hirst  experimenting  at  Zermatt  on  the  turbid 
water  of  the  Visp,  which  was  charged  with  the  finely-divided 
matter  ground  down  by  the  glaciers.  When  kept  still  for 
a  day  or  so,  the  grosser  matter  sank,  but  the  finer  matter 
remained  suspended,  and  gave  a  distinctly  blue  tinge  to 
the  water.  The  blueness  of  certain  Alpine  lakes  has  been 
shown  to  be  in  part  due  to  this  cause.  Professor  Roscoe  has 
noticed  several  striking  cases  of  a  similar  kind.  In  a  very 
remarkable  paper  the  late  Principal  Forbes  showed  that 
steam  issuing  from  the  safety-valve  of  a  locomotive,  when 
favorably  observed,  exhibits  at  a  certain  stage  of  its  con- 
densation the  colors  of  the  sky.  It  is  blue  by  reflected 
light,  and  orange  or  red  by  transmitted  light.  The  same 
effect,  as  pointed  out  by  Goethe,  is  to  some  extent  ex- 
hibited by  peat-smoke.  More  than  ten  years  ago  I  amused 
myself  at  Killarney  by  observing  on  a  calm  day  the  straight 
smoke-columns  rising  from  the  cabin  chimneys.  It  was 
easy  to  project  the  lower  portion  of  a  column  against  a 
dark  pine,  and  its  upper  portion  against  a  bright  cloud. 
The  smoke  in  the  former  case  was  blue,  being  seen  mainly 
by  reflected  light ;  in  the  latter  case  it  was  reddish,  being 
seen  mainly  by  transmitted  light.  Such  smoke  was  not  in 
exactly  the  condition  to  give  us  the  glow  of  the  Alps, 
but  it  was  a  step  in  this  direction.  Brticke's  fine  pre- 
cipitate above  referred  to  koks  yellowish  by  transmitted 

von  der  Rosskastanie,  man  stecke  denselben  in  ein  Glas  Wasser,  und  in 
der  kiirzesten  Zeit  werden  wir  das  vollkommenste  Himmelblau  entstchcn 
sehen." — Goethe's  Werlce,  b.  xxix.,  p.  24. 


SCIENTIFIC   USE   OF  THE  IMAGINATION.  145 

light,  but  by  duly  strengthening  the  precipitate  you  may 
render  the  white  light  of  noon  as  ruby-colored  as  the  sun 
when  seen  through  Liverpool  smoke,  or  upon  Alpine  hori- 
zons. I  do  not,  however,  point  to  the  gross  smoke  arising 
from  coal  as  an  illustration  of  the  action  of  small  particles, 
because  such  smoke  soon  absorbs  and  destroys  the  waves 
of  blue  instead  of  sending  them  to  the  eyes  of  the  observer. 
These  multifarious  facts,  and  numberless  others  which 
cannot  now  be  referred  to,  are  explained  by  reference  to 
the  single  principle,  that  where  the  scattering  particles  are 
small  in  comparison  to  the  size  of  the  waves  w^e  have  in 
the  reflected  light  a  greater  proportion  of  the  smaller 
waves,  and  in  the  transmitted  light  a  greater  proportion 
of  the  larger  waves,  than  existed  in  the  original  white 
light.  The  physiological  consequence  is  that  in  the  one 
light  blue  is  predominant,  and  in  the  other  light  orange 
or  red.  And  now  let  us  push  our  inquiries  forward. 
Our  best  microscopes  can  readily  reveal  objects  not  more 
than  -^-g-o-oth  of  an  inch  in  diameter.  This  is  less  than 
the  length  of  a  wave  of  red  light.  Indeed,  a  first-rate 
microscope  would  enable  us  to  discern  objects  not  exceed- 
ing in  diameter  the  length  of  the  smallest  waves  of  the 
visible  spectrum.  By  the  microscope,  therefore,  we  can 
submit  our  particles  to  an  experimental  test.  If  they  are 
as  large  as  the  light-waves  they  will  infallibly  be  seen : 
and  if  they  are  not  seen  it  is  because  they  are  smaller.  I 
placed  in  the  hands  of  our  President  a  bottle  containing 
Briicke's  particles  in  greater  number  and  coarseness  than 
those  examined  by  Brticke  himself.  The  liquid  was  a 
milky  blue,  and  Mr.  Huxley  applied  to  it  his  highest 
microscopic  power.  He  satisfied  me  at  the  time  that  had 
particles  of  even  I0o1o0oth  of  an  inch  in  diameter  existed 
in  the  liquid  they  could  riot  have  escaped  detection.  But 
no  particles  were  seen.  Under  the  microscope  the  turbid 
liquid  was  not  to  be  distinguished  from  distilled  water. 
7 


146  FRAGMENTS  OF  SCIENCE. 

Briicke,  I  may  say,  also  found  the  particles  to  be  of  ultra- 
microscopic  magnitude. 

But  we  have  it  in  our  power  to  imitate  far  more  closely 
than  we  have  hitherto  done  the  natural  conditions  of  this 
problem.  "We  can  generate  in  air,  as  many  of  you  know, 
artificial  skies,  and  prove  their  perfect  identity  with  the 
natural  one,  as  regards  the  exhibition  of  a  number  of 
wholly  unexpected  phenomena.  By  a  continuous  process 
of  growth,  moreover,  we  are  able  to  connect  sky-matter, 
if  I  may  use  the  term,  with  molecular  matter  on  the  one 
side,  and  with  molar  matter,  or  matter  in  sensible  masses, 
on  the  other.  In  illustration  of  this,  I  will  take  an  ex- 
periment described  by  M.  Morren  of  Marseilles  at  the  last 
meeting  of  the  British  Association.  Sulphur  and  oxygen 
combine ,  to  form  sulphurous  acid  gas.  It  is  this  choking 
gas  that  is  smelt  when  a  sulphur-match  is  burnt  in  air. 
Two  atoms  of  oxygen  and  one  of  sulphur  constitute  the 
molecule  of  sulphurous  acid.  Now  it  has  been  recently 
shown  in  a  great  number  of  instances  that  waves  of  ether 
issuing  from  a  strong  source,  such  as  the  sun  or  the 
electric  light,  are  competent  to  shake  asunder  the  atoms 
of  gaseous  molecules.  A  chemist  would  call  this  "  decom- 
position" by  light;  but  it  behooves  us,  who  are  examin- 
ing the  power  and  function  of  the  imagination,  to  keep 
constantly  before  us  the  physical  images  which  underlie 
our  terms.  Therefore,  I  say,  sharply  and  definitely,  that 
the  components  of  the  molecules  of  sulphurous  acid  are 
shaken  asunder  by  the  ether-waves.  Enclosing  the  sub- 
stance in  a  suitable  vessel,  placing  it  in  a  dark  room,  and 
sending  through  it  a  powerful  beam  of  light,  we  at  first 
see  nothing :  the  vessel  containing  the  gas  is  as  empty 
as  a  vacuum.  Soon,  however,  along  the  track  of  the 
beam  a  beautiful  sky-blue  color  is  observed,  which  is 
due  to  the  liberated  particles  of  sulphur.  For  a  time 
the  blue  grows  more  intense ;  it  then  becomes  whitish ; 


SCIENTIFIC   USE   OF   THE   IMAGINATION.  147 

and  from  a  whitish  blue  it  passes  to  a  more  or  less  perfect 
white.  If  the  action  be  continued  long  enough,  we  end 
by  filling  the  tube  with  a  dense  cloud  of  sulphur-particles, 
which  by  the  application  of  proper  means  may  be  rendered 
visible. 

Here,  then,  our  ether-waves  untie  the  bond  of  chemical 
affinity,  and  liberate  a  body — sulphur — which  at  ordinary 
temperatures  is  a  solid,  and  which  therefore  soon  becomes 
an  object  of  the  senses.  We  have  first  of  all  the  free 
atoms  of  sulphur,  which  are  both  invisible  and  incompetent 
to  stir  the  retina  sensibly  with  scattered  light.  But  these 
atoms  gradually  coalesce  and  form  particles,  which  grow 
larger  by  continual  accretion,  until  after  a  minute  or  two 
they  appear  as  sky-matter.  In  this  condition  they  are  in- 
visible themselves,  but  competent  to  send  an  amount  of 
wave-motion  to  the  retina  sufficient  to  produce  the  fir- 
mamental  blue.  The  particles  continue,  or  may  be  caused 
to  continue,  in  this  condition  for  a  considerable  time, 
during  which  no  microscope  can  cope  with  them.  But 
they  continually  grow  larger,  and  pass  by  insensible  grada- 
tions into  the  state  of  cloud,  when  they  can  no  longer  elude 
the  armed  eye.  Thus  without  solution  of  continuity  we 
start  with  matter  in  the  molecule,  and  end  with  matter  in 
the  mass,  sky-matter  being  the  middle  term  of  the  series  of 
transformations. 

Instead  of  sulphurous  acid,  we  might  choose  from  a 
dozen  other  substances,  and  produce  the  same  effect  with 
any  of  them.  In  the  case  of  some — probably  in  the  case 
of  all — it  is  possible  to  preserve  matter  in  the  skyey  con- 
dition for  fifteen  or  twenty  minutes  under  the  continual 
operation  of  the  light.  During  these  fifteen  or  twenty 
minutes  the  particles  are  constantly  growing  larger,  with- 
out ever  exceeding  the  size  requisite  to  the  production  of 
the  celestial  blue.  Now,  when  two  vessels  are  placed  be- 
fore you,  each  containing  sky-matter,  it  is  possible  to  state 


148  FRAGMENTS  OF   SCIENCE. 

with  great  distinctness  which  vessel  contains  the  largest 
particles.  The  retina  is  very  sensitive  to  differences  of 
light,  when,  as  here,  the  eye  is  in  comparative  darkness, 
and  when  the  quantities  of  wave-motion  thrown  against 
the  retina  are  small.  The  larger  particles  declare  them- 
selves by  the  greater  whiteness  of  their  scattered  light. 
Call  now  to  mind  the  observation,  or  effort  at  observation, 
made  by  our  President,  when  he  failed  to  distinguish  the 
particles  of  mastic  in  Brticke's  medium,  and  when  you  have 
done  so  follow  me.  I  permitted  a  beam  of  light  to  act 
upon  a  certain  vapor.  In  two  minutes  the  azure  appeared, 
but  at  the  end  of  fifteen  minutes  it  had  not  ceased  to  be 
azure.  After  fifteen  minutes,  for  example,  its  color,  and 
some  other  phenomena,  pronounced  it  to  be  a  blue  of  dis- 
tinctly smaller  particles  than  those  sought  for  in  vain  by 
Mr.  Huxley.  These  particles,  as  already  stated,  must  have 
been  less  than  1 0  ^  0  Oth  of  an  inch  in  diameter.  And  now 
I  want  you  to  submit  to  your  imagination  the  following 
question:  Here  are  particles  which  have  been  growing 
continually  for  fifteen  minutes,  and  at  the  end  of  that  time 
are  demonstrably  smaller  than  those  which  defied  the  mi- 
croscope of  Mr.  Huxley :  what  must  have  been  the  size  of 
these  particles  at  the  beginning  of  their  growth  ?  What 
notion  can  you  form  of  the  magnitude  of  such  particles  ? 
The  distances  of  stellar  space  give  us  simply  a  bewildering 
sense  of  vastness  without  leaving  any  distinct  impression 
on  the  mind,  and  the  magnitudes  with  which  we  have  here 
to  do  bewilder  us  equally  in  the  opposite  direction.  We 
are  dealing  with  infinitesimals  compared  with  which  the 
test  objects  of  the  microscope  are  literally  immense. 

From  their  perviousness  to  stellar  light  and  other  con- 
siderations, Sir  John  Herschel  drew  some  startling  conclu- 
sions regarding  the  density  and  weight  of  comets.  You 
know  that  these  extraordinary  and  mysterious  bodies  some- 
times throw  out  tails  100,000,000  of  miles  in  length,  and 


SCIENTIFIC  USE  OF  THE  IMAGINATION.  149 

50,000  miles  in  diameter.  The  diameter  of  our  earth  is 
8,000  miles.  Both  it  and  the  sky,  and  a  good  portion  of 
space  beyond  the  sky,  would  certainly  be  included  in  a 
sphere  10,000  miles  across.  Let  us  fill  a  hollow  sphere  of 
this  diameter  with  cometary  matter,  and  make  it  our  unit 
of  measure.  To  produce  a  comet's  tail  of  the  size  just  men- 
tioned, about  300,000  such  measures  would  have  to  be 
emptied  into  space.  Now,  suppose  the  whole  of  this  stuff 
to  be  swept  together  and  suitably  compressed,  what  do  you 
suppose  its  volume  would  be  ?  Sir  John  Herschel  would 
probably  tell  you  that  the  whole  mass  might  be  carted 
away  at  a  single  effort  by  one  of  your  dray-horses.  In  fact, 
I  do  not  know  that  he  would  require  more  than  a  small 
fraction  of  a  horse-power  to  remove  the  cometary  dust. 
After  this  you  will  hardly  regard  as  monstrous  a  notion  I 
have  sometimes  entertained  concerning  the  quantity  of 
matter  in  our  sky.  Suppose  a  shell  to  surround  the  earth 
at  a  height  above  the  surface  which  would  place  it  beyond 
the  grosser  matter  that  hangs  in  the  lower  regions  of  the 
air — say  at  the  height  of  the  Matterhorn  or  Mont  Blanc. 
Outside  this  shell  we  have  the  deep-blue  firmament.  Let 
the  atmospheric  space  beyond  the  shell  be  swept  clean,  and 
let  the  sky-matter  be  properly  gathered  up.  What  is  its 
probable  amount  ?  I  have  sometimes  thought  that  a  lady's 
portmanteau  would  contain  it  all.  I  have  thought  that 
even  a  gentleman's  portmanteau — possibly  his  snuff-box — 
might  take  it  in.  And  whether  the  actual  sky  be  capable 
of  this  amount  of  condensation  or  not,  I  entertain  no  doubt 
that  a  sky  quite  as  vast  as  ours,  and  as  good  in  appearance, 
could  be  formed  from  a  quantity  of  matter  which  might  be 
held  in  the  hollow  of  the  hand. 

Small  in  mass,  the  vastness  in  point  of  number  of  the 
particles  of  our  sky  may  be  inferred  from  the  continuity  of 
its  light.  It  is  not  in  broken  patches,  nor  at  scattered  points 
that  the  heavenly  azure  is  revealed.  To  the  observer  on 


150  FRAGMENTS  OF  SCIENCE. 

the  summit  of  Mont  Blanc  the  blue  is  as  uniform  and  co- 
herent as  if  it  formed  the  surface  of  the  most  close-grained 
solid.  A  marble  dome  would  not  exhibit  a  stricter  con- 
tinuity. And  Mr.  Glaisher  will  inform  you  that  if  our  hy- 
pothetical shell  were  lifted  to  twice  the  height  of  Mont 
Blanc  above  the  earth's  surface,  we  should  still  have  the 
azure  overhead.  Everywhere  through  the  atmosphere  those 
sky-particles  are  strewn.  They  fill  the  Alpine  valleys, 
spreading  like  a  delicate  gauze  in  front  of  the  slopes  of 
pine.  They  sometimes  so  swathe  the  peaks  with  light  as 
to  abolish  their  definition.  This  year  I  have  seen  the 
Weisshorn  thus  dissolved  in  opalescent  air.  By  proper 
instruments  the  glare  thrown  from  the  sky-particles  against 
the  retina  may  be  quenched,  and  then  the  mountain  which 
it  obliterated  starts  into  sudden  definition.  Its  extinction 
in  front  of  a  dark  mountain  resembles  exactly  the  with- 
drawal of  a  veil.  It  is  the  light  then  taking  possession  of 
the  eye,  and  not  the  particles  acting  as  opaque  bodies,  that 
interferes  with  the  definition.  By  day  this  light  quenches 
the  stars ;  even  by  moonlight  it  is  able  to  exclude  from 
vision  all  stars  between  the  fifth  and  the  eleventh  magni- 
.,-  tude.  It  may  be  likened  to  a  noise,  and  the  stellar  radiance 
to  a  whisper  drowned  by  the  noise. 

What  is  tl^  nature  of  the  particles  which  shed  this 
light  ?  The  celebrated  De  la  Rive  ascribes  the  haze  of  the 
Alps  in  fine  weather  to  floating  organic  germs.  Now,  the 
possible  existence  of  germs  in  such  profusion  has  been  held 
up  as  an  absurdity.  It  has  been  affirmed  that  they  would 
darken  the  air,  and  on  the  assumed  impossibility  of  their 
existence  in  the  requisite  numbers,  without  invasion  of  the 
solar  light,  a  powerful  argument  has  been  based  by  be- 
lievers in  spontaneous  generation.  Similar  arguments 
have  been  used  by  the  opponents  of  the  germ  theory  of 
epidemic  disease,  who  have  triumphantly  challeged  an  ap- 
peal to  the  microscope  and  the  chemist's  balance  to  decide 


SCIENTIFIC  USE   OF  THE  IMAGINATION.  151 

the  question.  Such  arguments  are  absolutely  valueless. 
Without  committing  myself  in  the  least  to  De  la  Rive's 
notion,  without  offering  any  objection  here  to  the  doctrine 
of  spontaneous  generation,  without  expressing  any  adhe- 
rence to  the  germ  theory  of  disease,  I  would  simply  draw 
attention  to  the  fact  that  in  the  atmosphere  we  have  parti- 
cles which  defy  both  the  microscope  and  the  balance,  which 
do  not  darken  the  air,  and  which  exist,  nevertheless,  in 
multitudes  sufficient  to  reduce  to  insignificance  the  Israel- 
itish  hyperbole  regarding  the  sands  upon  the  sea-shore. 

The  varying  judgments  of  men  on  these  and  other  ques- 
tions may  perhaps  be,  to  some  extent,  accounted  for  by 
that  doctrine  of  relativity  which  plays  so  important  a  part 
in  philosophy.  This  doctrine  affirms  that  the  impressions 
made  upon  us  by  any  circumstance,  or  combination  of  cir- 
cumstances, depend  upon  our  previous  state.  Two  travellers 
upon  the  same  peak,  the  one  having  ascended  to  it  from 
the  plain,  the  other  having  descended  to  it  from  a  higher 
elevation,  will  be  differently  affected  by  the  scene  around 
them.  To  the  one  Nature  is  expanding,  to  the  other  it  is 
contracting,  and  feelings  are  sure  to  differ  which  have  two 
such  different  antecedent  states.  In  our  scientific  judg- 
ments the  law  of  relativity  may  also  play  an  important  part. 
To  two  men,  one  educated  in  the  school  of  the  senses,  who 
has  mainly  occupied  himself  with  observation,  and  the  other 
educated  in  the  school  of  imagination  as  well,  and  exercised 
in  the  conceptions  of  atoms  and  molecules,  to  which  we 
have  so  frequently  referred,  a  bit  of  matter,  say  -^^th  of 
of  an  inch  in  diameter,  will  present  itself  differently.  The 
one  descends  to  it  from  his  molar  heights,  the  other  climbs 
to  it  from  his  molecular  low-lands.  To  the  one  it  appears 
small,  to  the  other  large.  So  also  as  regards  the  apprecia- 
tion of  the  most  minute  forms  of  life  revealed  by  the  micro- 
scope. To  one  of  these  men  they  naturally  appear  conter- 
minous with  the  ultimate  particles  of  matter,  and  he  readily 


152  FRAGMENTS  OF  SCIENCE. 

figures  the  molecules  from  which  they  directly  spring ;  with 
him  there  is  but  a  step  from  the  atom  to  the  organism. 
The  other  discerns  numberless  organic  gradations  between 
both.  Compared  with  his  atoms,  the  smallest  vibrios  and 
bacteria  of  the  microscopic  fielcl  are  as  behemoth  and  levia- 
than. The  law  of  relativity  may  to  some  extent  explain 
the  different  attitudes  of  these  two  men  with  regard  to  the 
question  of  spontaneous  generation.  An  amount  of  evi- 
dence which  satisfies  the  one  entirely  fails  to  satisfy  the 
other ;  and  while  to  the  one  the  last  bold  defence  and  start- 
ling expansion  of  the  doctrine  will  appear  perfectly  conclu- 
sive, to  the  other  it  will  present  itself  as  imposing  a  profit- 
less labor  of  demolition  on  subsequent  investigators.1 

I  trust,  Mr.  President,  that  you — whom  untoward  circum- 
stances have  made  a  biologist,  but  who  still  keep  alive  your 
sympathy  with  that  class  of  inquiries  which  Nature  intend- 
ed you  to  pursue  and  adorn — will  excuse  me  to  your  breth- 
ren if  I  say  that  some  of  them  seem  to  form  an  inadequate 
estimate  of  the  distance  which  separates  the  microscopic 
from  the  molecular  limit,  and  that,  as  a  consequence,  they 
sometimes  employ  a  phraseology  which  is  calculated  to  mis- 
lead. When,  for  example,  the  contents  of  a  cell  are  de- 
scribed as  perfectly  homogeneous,  as  absolutely  structure- 
less, because  the  microscope  fails  to  distinguish  any  struct- 
ure, then  I  think  the  microscope  begins  to  play  a  mischiev^ 
ous  part.  A  little  consideration  will  make  it  plain  to  all 
of  you  that  the  microscope  can  have  no  voice  in  the  real 
question  of  germ-structure.  Distilled  water  is  more  per- 
fectly homogeneous  than  the  contents  of  any  possible  or- 
ganic germ.  What  causes  the  liquid  to  cease  contracting 
at  39°  Fahrenheit,  and  to  expand  until  it  freezes  ?  It  is  a 
structural  process  of  which  the  microscope  can  take  no 
note,  nor  is  it  likely  to  do  so  by  any  conceivable  extension 

1  A  resolute  scrutiny  of  the  experiments,  recently  executed  with 
reference  to  this  question,  is  sure  to  yield  i  instructive  results. 


SCIENTIFIC   USE   OF  THE  IMAGINATION.  153 

of  its  powers.  Place  this  distilled  water  in  the  field  of  an 
electro-magnet,  and  bring  a  microscope  to  bear  upon  it. 
Will  any  change  be  observed  when  the  magnet  is  excited  ? 
Absolutely  none ;  and  still  profound  and  complex  changes 
have  occurred.  First  of  all,  the  particles  of  water  are  ren- 
dered diamagneticallj  polar ;  and  secondly,  in  virtue  of  the 
structure  impressed  upon  it  by  the  magnetic  strain  of  its 
molecules,  the  liquid  twists  a  ray  of  light  in  a  fashion  per- 
fectly determinate  both  as  to  quantity  and  direction.  It 
would  be  immensely  interesting  to  both  you  and  me  if  one 
whom  I  hoped  to  see  here  present,1  who  has  brought  his 
brilliant  imagination  to  bear  upon  this  subject,  could  make 
us  see  as  he  sees  the  entangled  molecular  processes  involved 
in  the  rotation  of  the  plane  of  polarization  by  magnetic 
force.  While  dealing  with  this  question,  he  lived  in  a  world 
of  matter  and  of  motion,  to  which  the  microscope  has  no 
passport,  and  in  which  it  can  offer  no  aid.  The  cases  in 
which  similar  conditions  hold  are  simply  numberless.  Have 
the  diamond,  the  amethyst,  and  the  countless  other  crystals 
formed  in  the  laboratories  of  Nature  and  of  man  no  struct- 
ure ?  Assuredly  they  have ;  but  what  can  the  microscope 
make  of  it  ?  Nothing.  It  cannot  be  too  distinctly  borne 
in  mind  that  between  the  microscope  limit  and  the  true 
molecular  limit  there  is  room  for  infinite  permutations  and 
combinations.  It  is  in  this  region  that  the  poles  of  the 
atoms  are  arranged,  that  tendency  is  given  to  their  powers, 
so  that  when  these  poles  and  powers  have  free  action  and 
proper  stimulus  in  a  suitable  environment,  they  determine 
first  the  germ,  and  afterward  the  complete  organism.  This 
first  marshalling  of  the  atoms  on  which  all  subsequent  ac- 
tion depends  baffles  a  keener  power  than  that  of  the  micro- 
scope. Through  pure  excess  of  complexity,  and  long  be- 
fore observation  can  have  any  voice  in  the  matter,  the  most 
highly-trained  intellect,  the  most  refined  and  disciplined 

1  Sir  William  Thomson 


154  FKAGMENTS  OF  SCIENCE. 

imagination,  retires  in  bewilderment  from  the  contempla- 
tion of  the  problem.  "We  are  struck  dumb  by  an  astonish- 
ment which  no  microscope  can  relieve,  doubting  not  only 
the  power  of  our  instrument,  but  even  whether  we  ourselves 
possess  the  intellectual  elements  which  will  ever  enable  us 
to  grapple  with  the  ultimate  structural  energies  of  Nature. 
But  the  speculative  faculty,  of  which  imagination  forms 
so  large  a  part,  will  nevertheless  wander  into  regions  where 
the  hope  of  certainty  would  seem  to  be  entirely  shut  out. 
We  think  that  though  the  detailed  analysis  may  be,  and 
may  forever  remain,  beyond  us,  general  notions  may  be  at- 
tainable. At  all  events,  it  is  plain  that  beyond  the  present 
outposts  of  microscopic  inquiry  lies  an  immense  field  for 
the  exercise  of  the  speculative  power.  It  is  only,  however, 
the  privileged  spirits  who  know  how  to  use  their  liberty 
without  abusing  it,  who  are  able  to  surround  imagination 
by  the  firm  frontiers  of  reason,  that  are  likely  to  work  with 
any  profit  here.  But  freedom  to  them  is  of  such  paramount 
importance  that,  for  the  sake  of  securing  it,  a  good  deal  of 
wildness  on  the  part  of  weaker  brethren  may  be  overlooked. 
In  more  senses  than  one  Mr.  Darwin  has  drawn  heavily 
upon  the  scientific  tolerance  of  his  age.  He  has  drawn 
heavily  upon  time  in  his  development  of  species,  and  he  has 
drawn  adventurously  upon  matter  in  his  theory  of  pangen- 
esis.  According  to  this  theory,  a  germ  already  microscopic 
is  a  world  of  minor  germs.  Not  only  is  the  organism  as  a 
whole  wrapped  up  in  the  germ,  but  every  organ  of  the  or- 
ganism has  there  its  special  seed.  This,  I  say,  is  an  adven- 
turous draft  on  the  power  of  matter  to  divide  itself  and 
distribute  its  forces.  But,  unless  we  are  perfectly  sure  that 
he  is  overstepping  the  bounds  of  reason,  that  he  is  unwit- 
tingly sinning  against  observed  fact  or  demonstrated  law — 
for  a  mind  like  that  of  Darwin  can  never  sin  wittingly 
against  either  fact  or  law — we  ought,  I  think,  to  be  cautious 
in  limiting  his  intellectual  horizon.  If  there  be  the  least 


SCIENTIFIC  USE  OF  THE  IMAGINATION.  155 

doubt  in  the  matter,  it  ought  to  be  given  in  favor  of  the 
freedom  of  such  a  mind.  To  it  a  vast  possibility  is  in  it- 
self a  dynamic  power,  though  the  possibility  may  never 
be  drawn  upon.  It  gives  me  pleasure  to  think  that  the 
facts  and  reasonings  of  this  discourse  tend  rather  toward 
the  justification  of  Mr.  Darwin  than  toward  his  condemna- 
tion, that  they  tend  rather  to  augment  than  to  diminish  the 
cubic  space  demanded  by  this  soaring  speculator ;  for  they 
seem  to  show  the  perfect  competence  of  matter  and  force, 
as  regards  divisibility  and  distribution,  to  bear  the  heaviest 
strain  that  he  has  hitherto  imposed  upon  them. 

In  the  case  of  Mr.  Darwin,  observation,  imagination,  and 
reason  combined,  have  run  back  W7ith  wonderful  sagacity 
and  success  over  a  certain  length  of  the  line  of  biological 
succession.  Guided  by  analogy,  in  his  "  Origin  of  Species," 
he  placed  at  the  root  of  life  a  primordial  germ,  from  which 
he  conceived  the  amazing  richness  and  variety  of  the  life 
that  now  is  upon  the  earth's  surface  might  be  deduced.  If 
this  hypothesis  were  true,  it  would  not  be  final.  The  hu- 
man imagination  would  infallibly  look  behind  the  germ, 
and,  however  hopeless  the  attempt,  would  inquire  into  the 
history  of  its  genesis.  In  this  dim  twilight  of  conjecture 
the  searcher  welcomes  every  gleam,  and  seeks  to  augment 
his  light  by  indirect  incidences.  He  studies  the  methods 
of  Nature  in  the  ages  and  the  worlds  within  his  reach,  in 
order  to  shape  the  course  of  speculation  in  the  antecedent 
ages  and  worlds.  And  though  the  certainty  possessed  by 
experimental  inquiry  is  here  shut  out,  the  imagination  is 
not  left  entirely  without  guidance.  From  the  examination 
of  the  solar  system,  Kant  and  Laplace  came  to  the  conclu- 
sion that  its  various  bodies  once  formed  parts  of  the  same 
undislocated  mass  ;  that  matter  in  a  nebulous  form  preceded 
matter  in  a  dense  form ;  that  as  the  ages  rolled  away,  heat 
was  wasted,  condensation  followed,  planets  were  detached, 
and  that  finally  the  chief  portion  of  the  fiery  cloud  reached, 


156  FRAGMENTS  OF  SCIENCE. 

by  self-compression,  the  magnitude  and  density  of  our  sun. 
Tlie  earth  itself  offers  evidence  of  a  fiery  origin ;  and  in  our 
day  the  hypothesis  of  Kant  and  Laplace  receives  the  inde- 
pendent countenance  of  spectrum  analysis,  which  proves 
the  same  substances  to  be  common  to  the  earth  and  sun. 

Accepting  some  such  view  of  the  construction  of  our 
system  as  probable,  a  desire  immediately  arises  to  connect 
the  present  life  of  our  planet  with  the  past.  "We  wish  to 
know  something  of  our  remotest  ancestry.  On  its  first  de- 
tachment from  the  central  mass,  life,  as  we  understand  it, 
could  hardly  have  been  present  on  the  earth.  How,  then, 
did  it  come  there  ?  The  thing  to  be  encouraged  here  is 
a  reverent  freedom — a  freedom  preceded  by  the  hard  disci- 
pline which  checks  licentiousness  in  speculation — while  the 
thing  to  be  repressed,  both  in  science  and  out  of  it,  is  dog- 
matism. And  here  I  am  in  the  hands  of  the  meeting — 
willing  to  end,  but  ready  to  go  on.  I  have  no  right  to  in- 
trude upon  you,  unasked,  the  unformed  notions  which  are 
floating  like  clouds,  or  gathering  to  more  solid  consistency 
in  the  modern  speculative  scientific  mind.  But  if  you  wish 
me  to  speak  plainly,  honestly,  and  undisputatiously,  I  am 
willing  to  do  so.  On  the  present  occasion — 

"  You  are  ordained  to  call,  and  I  to  come." 

Two  views,  then,  offer  themselves  to  us.  Life  was  pres- 
ent potentially  in  matter  when  in  the  nebulous  form,  and 
was  unfolded  from  it  by  the  way  of  natural  development, 
or  it  is  a  principle  inserted  into  matter  at  a  later  date.  With 
regard  to  the  question  of  time,  the  views  of  men  have 
changed  remarkably  in  our  day  and  generation ;  and  I 
must  say  as  regards  courage  also,  and  a  manful  willingness 
to  engage  in  open  contest,  with  fair  weapons,  a  great 

•change  has  also  occurred.  The  clergy  of  England — at  all 
events  the  clergy  of  London — have  nerve  enough  to  listen 
to  the  strongest  views  which  any  one  among  us  would  care 


SCIENTIFIC  USE   OF  THE  IMAGINATION.  157 

to  utter ;  and  they  invite,  if  they  do  not  challenge,  men  of 
the  most  decided  opinions  to  state  and  stand  by  those  opin- 
ions in  open  court.  Let  the  hardiest  theory  be  stated  only 
in  the  language  current  among  gentlemen,  and  they  look  it 
in  the  face ;  smiting  the  theory,  if  they  do  not  like  it,  not 
with  theologicfulrnination,  but  with  honest  secular  strength. 
With  the  country  clergy  I  am  told  the  case  is  different.  It 
is  right  that  I  should  say  this,  because  the  clergy  of  Lon- 
don have  more  than  once  offered  me  the  chance  of  meeting 
them  in  open,  honorable  discussion. 

Two  or  three  years  ago,  in  an  ancient  London  College, 
I  listened  to  such  a  discussion  at  the  end  of  a  remarkable 
lecture  by  a  very  remarkable  man.  Three  or  four  hundred 
clergymen  were  present  at  the  lecture.  The  orator  began 
with  the  civilization  of  Egypt  in  the  time  of  Joseph ; 
pointing  out  that  the  very  perfect  organization  of  the 
kingdom,  and  the  possession  of  chariots,  in  one  of  which 
Joseph  rode,  indicated  a  long  antecedent  period  of  civili- 
zation. He  then  passed  on  to  the  mud  of  the  Nile,  its 
rate  of  augmentation,  its  present  thickness,  and  the  re- 
mains of  human  handiwork  found  therein ;  thence  to  the 
rocks  which  bound  the  Nile  valley,  and  which  teem  with 
organic  remains.  Thus  in  his  own  clear  and  admirable 
way  he  caused  the  idea  of  the  world's  age  to  expand  itself 
indefinitely  before  the  mind  of  his  audience,  and  he  con- 
trasted this  with  the  age  usually  assigned  to  the  world. 
During  his  discourse  he  seemed  to  be  swimming  against 
the  stream ;  he  manifestly  thought  that  he  was  opposing 
a  general  conviction.  He  expected  resistance ;  so  did  I. 
But  it  was  all  a  mistake :  there  was  no  adverse  current, 
o  opposing  conviction,  no  resistance,  merely  here  and 
there  a  half-humorous,  but  unsuccessful  attempt  to  entan- 
gle him  in  his  talk.  The  meeting  agreed  with  all  that 
had  been  said  regarding  the  antiquity  of  the  earth  and  of 
its  life.  They  had,  indeed,  known  it  all  long  ago,  and 


158  FRAGMENTS  OF  SCIENCE. 

they  good-humoredly  rallied  the  lecturer  for  coming  among 
them  with  so  stale  a  story.  It  was  quite  plain  that  this 
large  body  of  clergymen,  who  were,  I  should  say,  the  finest 
samples  of  their  class,  had  entirely  given  up  the  ancient 
landmarks,  and  transported  the  conception  of  life's  origin 
to  an  indefinitely  distant  past. 

^-  This  leads  us  to  the  gist  of  our  present  inquiry,  which 
is  this  :  Does  life  belong  to  what  we  call  matter,  or  is  it  an 
independent  principle  inserted  into  matter  at  some  suitable 
epoch — say  when  the  physical  conditions  became  such  as  to 
permit  of  the  development  of  life  ?  Let  us  put  the  ques- 
tion with  all  the  reverence  due  to  a  faith  and  culture  in 
which  we  all  were  cradled — a  faith  and  culture,  moreover, 
which  are  the  undeniable  historic  antecedents  of  our  pres- 
ent enlightenment.  I  say,  let  us  put  the  question  rever- 
ently, but  let  us  also  put  it  clearly  and  definitely.  There 
are  the  strongest  grounds  for  believing  that  during  a  cer- 
tain period  of  its  history  the  earth  was  not,  nor  was  it  fit 
to  be,  the  theatre  of  life.  Whether  this  was  ever  a  nebu- 
lous period,  or  merely  a  molten  period,  does  not  much 
matter ;  and  if  we  revert  to  the  nebulous  condition,  it  is 
because  the  probabilities  are  really  on  its  side.  Our  ques- 
tion is  this  :  Did  creative  energy  pause  until  the  nebulous 
matter  had  condensed,  until  the  earth  had  been  detached, 
until  the  solar  fire  had  so  far  withdrawn  from  the  earth's 
/  vicinity  as  to  permit  a  crust  to  gather  round  the  planet  ? 

.  Did  it  wait  until  the  air  was  isolated,  until  the  seas  were 
formed,  until  evaporation,  condensation,  and  the  descent  of 
rain  had  begun,  until  the  eroding  forces  of  the  atmosphere 
had  weathered  and  decomposed  the  molten  rocks  so  as  to 
form  soils,  until  the  sun's  rays  had  become  so  tempered  by 
distance  and  by  waste  as  to  be  chemically  fit  for  the  de- 
compositions necessary  to  vegetable  life  ?  Having  waited 
through  those  MOILS  until  the  proper  conditions  had  set  in, 
did  it  send  the  fiat  forth,  "  Let  Life  be  !  "  ?  These  ques- 


SCIENTIFIC   USE   OF  THE   IMAGINATION.  159 

tions  define  a  hypothesis  not  without  its  difficulties,  but 
the  dignity  of  which  was  demonstrated  by  the  nobleness 
of  the  men  whom  it  sustained. 

Modern  scientific  thought  is  called  upon  to  decide  be- 
tween this  hypothesis  and  another:  and  public  thought 
generally  will  afterward  be  called  upon  to  do  the  same. 
You  may,  however,  rest  secure  in  the  belief  that  the  hy- 
pothesis just  sketched  can  never  be  stormed,  and  that  it  is 
sure,  if  it  yield  at  all,  to  yield  to  a  prolonged  siege.  To 
gain  new  territory  modern  argument  requires  more  time 
than  modern  arms,  though  both  of  them  move  with  greater 
rapidity  than  of  yore.  But  however  the  convictions  of  indi- 
viduals here  and  there  may  be  influenced,  the  process  must 
be  slow  and  secular  which  commends  the  rival  hypothesis 
of  Natural  Evolution  to  the  public  mind.  For  what  are  the 
core  and  essence  of  this  hypothesis  ?  Strip  it  naked  and 
you  stand  face  to  face  with  the  notion  that  not  alone  the 
more  ignoble  forms  of  animalcular  or  animal  life,  not  alone 
the  nobler  forms  of  the  horse  and  lion,  not  alone  the  exqui- 
site and  wonderful  mechanism  of  the  human  body,  but  that 
the  human  mind  itself — emotion,  intellect,  will,  and  all  their 
phenomena — were  once  latent  in  a  fiery  cloud.  Surely 
the  mere  statement  of  such  a  notion  is  more  than  a  refu- 
tation. But  the  hypothesis  would  probably  go  even  further 
than  this.  Many  who  hold  it  would  probably  assent  to  the 
position  that  at  the  present  moment  all  our  philosophy,  all 
our  poetry,  all  our  science,  and  all  our  art — Plato,  Shake- 
speare, Newton,  and  Raphael — are  potential  in  the  fires  of 
the  sun.  We  long  to  learn  something  of  our  origin.  If 
the  Evolution  hypothesis  be  correct,  even  this  unsatisfied 
yearning  must  have  come  to  us  across  the  ages  which  sepa- 
rate the  unconscious  primeval  mist  from  the  consciousness 
of  to-day.  I  do  not  think  that  any  holder  of  the  Evolution 
hypothesis  would  say  that  I  overstate  it  or  overstrain  it  in 
any  way.  I  merely  strip  it  of  all  vagueness,  and  bring 


160  FRAGMENTS  OF  SCIENCE. 

before  you  unclothed  and  unvarnished  the  notions  by  which 
it  must  stand  or  fall. 

Surely  these  notions  represent  an  absurdity  too  mon- 
strous to  be  entertained  by  any  sane  mind.  Let  us,  how- 
ever, give  them  fair  play.  Let  us  steady  ourselves  in  front 
of  the  hypothesis,  and,  dismissing  all  terror  and  excitement 
from  our  minds,  let  us  look  firmly  into  it  with  the  hard  sharp 
eye  of  intellect  alone.  Why  are  these  notions  absurd,  and 
why  should  sanity  reject  them  ?  The  law  of  Relativity,  of 
which  we  have  previously  spoken,  may  find  its  application 
here.  These  Evolution  notions  are  absurd,  monstrous,  and 
fit  only  for  the  intellectual  gibbet,  in  relation  to  the  ideas 
concerning  matter  which  were  drilled  into  us  when  young. 
Spirit  and  matter  have  ever  been  presented  to  us  in  the 
rudest  contrast,  the  one  as  all-noble,  the  other  as  all-vile. 
But  is  this  correct  ?  Does  it  represent  what  our  mightiest 
spiritual  teacher  would  call  the  Eternal  Fact  of  the  Uni- 
verse ?  Upon  the  answer  to  this  question  all  depends. 
Supposing,  instead  of  having  the  foregoing  antithesis  of 
spirit  and  matter  presented  to  our  youthful  minds,  we  had 
been  taught  to  regard  them  as  equally  worthy  and  equally 
wonderful ;  to  consider  them  in  fact  as  two  opposite  faces 
of  the  self-same  mystery.  Supposing  that  in  youth  we  had 
been  impregnated  with  the  notion  of  the  poet  Goethe,  in- 
stead of  the  notion  of  the  poet  Young,  looking  at  matter, 
not  as  brute  matter,  but  as  "  the  living  garment  of  God ; " 
do  you  not  think  that  under  these  altered  circumstances 
the  law  of  Relativity  might  have  had  an  outcome  different 
from  its  present  one  ?  Is  it  not  probable  that  our  repug- 
nance to  the  idea  of  primeval  union  between  spirit  and 
matter  might  be  considerably  abated  ?  Without  this  total 
revolution  of  the  notions  now  prevalent,  the  Evolution  hy- 
pothesis must  stand  condemned ;  but  in  many  profoundly 
thoughtful  minds  such  a  revolution  has  already  taken  place. 
They  degrade  neither  member  of  the  mysterious  duality 


SCIENTIFIC  USE   OF  THE  IMAGINATION.  161 

referred  to ;  but  they  exalt  one  of  them  from  its  abasement, 
and  repeal  the  divorce  hitherto  existing  between  both.  In 
substance,  if  not  in  words,  their  position  as  regards  the 
relation  of  spirit  and  matter  is  :  "  What  God  hath  joined 
together  let  not  man  put  asunder."  And  with  regard  to 
the  ages  of  forge tfulness  which  lie  between  the  unconscious 
life  of  the  nebula  and  the  conscious  life  of  the  earth,  it  is, 
they  would  urge,  but  an  extension  of  that  forgetfulness 
which  preceded  the  birth  of  us  all. 

I  have  thus  led  you  to  the  outer  rim  of  speculative 
science,  for  beyond  the  nebulas  scientific  thought  has  never 
ventured  hitherto,  and  have  tried  to  state  that  which  I  con- 
sidered ought,  in  fairness,  to  be  outspoken.  I  do  not  think 
this  Evolution  hypothesis  is  to  be  flouted  away  contempt- 
"ously  ;  I  do  not  think  it  is  to  be  denounced  as  wicked.  It 
is  to  be  brought  before  the  bar  of  disciplined  reason,  and 
there  justified  or  condemned.  Let  us  hearken  to  those  who 
wisely  support  it,  and  to  those  who  wisely  oppose  it ;  and 
let  us  tolerate  those,  and  they  are  many,  who  foolishly  try 
to  do  either  of  these  things.  The  only  thing  out  of  place 
in  the  discussion  is  dogmatism  on  either  side.  Fear  not 
the  Evolution  hypothesis.  Steady  yourselves  in  its  presence 
upon  that  faith  in  the  ultimate  triumph  of  truth  which  was 
expressed  by  old  Gamaliel  when  he  said  :  "  If  it  be  of  God, 
ye  cannot  overthrow  it ;  if  it  be  of  man,  it  will  come  to 
naught."  Under  the  fierce  light  of  scientific  inquiry,  this 
hypothesis  is  sure  to  be  dissipated  if  it  possess  not  a  core 
of  truth.  Trust  me,  its  existence  as  a  hypothesis  in  the 
mind  is  quite  compatible  with  the  simultaneous  existence 
of  all  those  virtues  to  which  the  term  Christian  has  been 
applied.  It  does  not  solve — it  does  not  profess  to  solve — 
the  ultimate  mystery  of  this  universe.  It  leaves  in  fact 
that  mystery  untouched.  For  granting  the  nebula  and  its 
potential  life,  the  question,  whence  came  they  ?  would  still 
remain  to  baffle  and  bewilder  us.  At  bottom,  the  hypothe- 


162  FRAGMENTS  OF  SCIENCE. 

sis  does  nothing  more  than  "  transport  the  conception  of 
life's  origin  to  an  indefinitely  distant  past." 

Those  who  hold  the  doctrine  of  Evolution  are  by  no 
means  ignorant  of  the  uncertainty  of  their  data,  and  they 
yield  no  more  to  it  than  a  provisional  assent.  They  regard 
the  nebular  hypothesis  as  probable,  and  in  the  utter  absence 
of  any  evidence  to  prove  the  act  illegal,  they  extend  the 
method  of  Nature  from  tthe  present  into  the  past.  Here  the 
observed  uniformity  of  Nature  is  their  only  guide.  Within 
the  long  range  of  physical  inquiry,  they  have  never  dis- 
cerned in  Nature  the  insertion  of  caprice.  Throughout 
this  range  the  laws  of  physical  and  intellectual  continuity 
have  run  side  by  side.  Having  thus  determined  the  ele- 
ments of  their  curve  in  a  world  of  observation  and  experi- 
ment, they  prolong  that  curve  into  an  antecedent  world, 
and  accept  as  probable  the  unbroken  sequence  of  develop- 
ment from  the  nebula  to  the  present  time.  You  never  hear 
the  really  philosophical  defenders  of  the  doctrine  of  Uni- 
formity speaking  of  impossibilities  in  Nature.  They  never 
say,  what  they  are  constantly  charged  with  saying,  that  it 
is  impossible  for  the  Builder  of  the  universe  to  alter  His 
work.  Their  business  is  not  with  the  possible,  but  the 
actual — not  with  a  world  which  might  be,  but  with  a  world 
that  is.  This  they  explore  with  a  courage  not  unmixed 
with  reverence,  and  according  to  methods  which,  like  the 
'quality  of  a  tree,  are  tested  by  their  fruits.  They  have  but 
jine  desire — to  know  the  truth.  They  have  but  one  fear — 
lo  believe  a  lie.  And  if  they  know  the  strength  of  science, 
and  rely  upon  it  with  unswerving  trust,  they  also  know  the 
limits  beyond  which  science  ceases  to  be  strong.  They  best 
know  that  questions  offer  themselves  to  thought  which 
science,  as  now  prosecuted,  has  not  even  the  tendency  to 
solve.  They  keep  such  questions  open,  and  will  not  toler- 
ate any  unnecessary  limitation  of  the  horizon  of  their  souls. 
They  have  as  little  fellowship  with  the  atheist  who  says 


SCIENTIFIC  USE  OF  THE  IMAGINATION.  163 

there  is  no  God,  as  with  the  theist  who  professes  to  know 
the  mind  of  God.  "  Two  things,"  said  Immanuel  Kant, 
"  fill  me  with  awe :  the  starry  heavens  and  the  sense  of 
moral  responsibility  in  man."  And  in  his  hours  of  health 
and  strength  and  sanity,  when  the  stroke  of  action  has 
ceased  and  the  pause  of  reflection  has  set  in,  the  scientific 
investigator  finds  himself  overshadowed  by  the  same  awe. 
Breaking  contact  with  the  hampering  details  of  earth,  it 
associates  him  with  a  power  which  gives  fulness  and  tone 
to  his  existence,  but  which  he  can  neither  analyze  nor  com- 
prehend. 


A  TRANSLATION 

OF 

GOETHE'S  PROEMIUM  TO  "  GOTT  UND  WELT.' 


To  Him  who  from  eternity,  self-stirred, 
Himself  hath  made  by  His  creative  word  ! 
To  Him,  Supreme,  who  causeth  faith  to  be, 
Trust,  hope,  love,  power,  and  endless  energy  ! 
To  Him,  who,  seek  to  name  Him  as  we  will, 
UNKNOWN  within  Himself  abideth  still ! 

Strain  ear  and  eye,  till  sight  and  sense  be  dim ; 

Thou' It  find  but  faint  similitudes  of  Him : 

Yea,  and  thy  spirit  in  her  flight  of  flame 

Still  strives  to  gauge  the  symbol  and  the  name : 

Charmed  and  compelled  thou  climb'st  from  height  to  height, 

And'  round  thy  path  the  world  shines  wondrous  bright ; 

Time,  space,  and  size,  and  distance  cease  to  be, 

And  every  step  is  fresh  infinity. 

What  were  the  God  who  sat  outside  to  scan 

The  spheres  that  'neath  His  finger  circling  ran  ? 

God  dwells  within,  and  moves  the  world  and  moulds, 

Himself  and  Nature  in  one  form  enfolds : 

Thus  all  that  lives  in  Him,  and  breathes,  and  is, 

Shall  ne'er  His  puissance,  ne'er  His  spirit  miss. 

The  soul  of  man,  too,  is  a  universe  ; 

Whence  follows  it  that  race  with  race  concurs 

In  framing  all  it  knows  of  good  and  true 

God  ? — yea,  its  own  God  ;  and,  with  homage  due, 

Surrenders  to  His  sway  both  earth  and  heaven ; 

Fears  Him,  and  loves,  where  place  for  love  is  given. 

J.  A.  S. 
Spectator,  September  24,  1870. 


VIII. 
ON  RADIATION. 

THE     "REDE"    LECTURE. 

DELIVERED   IN   THE  SENATE-HOUSE  BEFORE  THE   UNIVERSITY  OF 
CAMBRIDGE. 

On  Tuesday,  May  16,  1865. 


"  Forsitan  et  rosea  Sol  alte  lampade  lucens, 
Possideat  multum  caecis  fervoribus  ignem 
Circum  se,  qui  sit  fulgore  notatus, 
-^stifer  ut  tantum  radiorum  exaugeat  ictum." 

Lucretius,  v.  610. 

"  Perhaps  too  the  sun  as  he  shines  aloft  with  rosy  lamp  has  round 
about  him  much  fire  with  heats  that  are  not  visible,  and  thus  the  fire  may 
be  marked  by  no  radiance,  so  that  fraught  with  heat  it  increases  to  such 
a  degree  the  stroke  of  the  rays." — Monro's  Translation. 

My  attention  was  drawn  to  this  remarkable  passage  by  the  late  ex- 
cellent and  accomplished  Sir  Edmund  Head,  Bart. 


VIII. 

RADIATION. 

1.    Visible  and  Invisible  Radiation. 

BETWEEN  the  mind  of  man  and  the  outer  world  are  in- 
terposed the  nerves  of  the  human  body,  which  translate, 
or  enable  the  mind  to  translate,  the  impressions  of  that 
world  into  facts  of  consciousness  and  thought. 

Different  nerves  are  suited  to  the  perception  of  different 
impressions.  We  do  not  see  with  the  ear,  nor  hear  with 
the  eye,  nor  are  we  rendered  sensible  of  sound  by  the 
nerves  of  the  tongue.  Out  of  the  general  assemblage  of 
physical  actions,  each  nerve,  or  group  of  nerves,  selects  and 
responds  to  those  for  the  perception  of  which  it  is  specially 
organized. 

The  optic  nerve  passes  from  the  brain  to  the  back  of 
the  eyeball  and  there  spreads  out,  to  form  the  retina,  a  web 
of  nerve  filaments,  on  which  the  images  of  external  objects 
are  projected  by  the  optical  portion  of  the  eye.  This  nerve 
is  limited  to  the  apprehension  of  the  phenomena  of  radia- 
tion, and,  notwithstanding  its  marvellous  sensibility  to 
certain  impressions  of  this  class,  it  is  singularly  obtuse  to 
other  impressions. 

Nor  does  the  optic  nerve  embrace  the  entire  range  even 
of  radiation.  Some  rays,  when  they  reach  it,  are  incom- 
petent to  evoke  its  power,  while  others  never  reach  it  at 
all,  being  absorbed  by  the  humors  of  the  eye.  To  all  rays 


168  FRAGMENTS  OF  SCIENCE. 

which,  whether  they  reach  the  retina  or  not,  fail  to  excite 
vision,  we  give  the  name  of  invisible  or  obscure  rays.  All 
non-luminous  bodies  emit  such  rays.  There  is  no  body  in 
Nature  absolutely  cold,  and  every  body  not  absolutely  cold 
emits  rays  of  heat.  But  to  render  radiant  heat  fit  to  affect 
the  optic  nerve  a  certain  temperature  is  necessary.  A  cool 
poker  thrust  into  a  fire  remains  dark  for  a  time,  but  when 
its  temperature  has  become  equal  to  that  of  the  surrounding 
coals  it  glows  like  them.  In  like  manner,  if  a  current  of 
electricity  of  gradually  increasing  strength  be  sent  through 
a  wire  of  the  refractory  metal  platinum,  the  wire  first  be- 
comes sensibly  warm  to  the  touch ;  for  a  time  its  heat  aug- 
ments, still,  however,  remaining  obscure ;  at  length  we  can 
no  longer  touch  the  metal  with  impunity ;  and  at  a  certain 
definite  temperature  it  emits  a  feeble  red  light.  As  the 
current  augments  in  power  the  light  augments  in  brilliancy, 
until  finally  the  wire  appears  of  a  dazzling  white.  The 
lio-ht  which  it  now  emits  is  similar  to  that  of  the  sun. 

O 

By  means  of  a  prism  Sir  Isaac  Newton  unravelled  the 
'texture  of  solar  light,  and  by  the  same  simple  instrument 
we  can  investigate  the  luminous  changes  of  our  platinum 
wire.  In  passing  through  the  prism  all  its  rays  (and  they 
are  infinite  in  variety)  are  bent  or  refracted  from  their 
straight  course ;  and  as  different  rays  are  differently  re- 
fracted by  the  prism,  we  are  by  it  enabled  to  separate  one 
class  of  rays  from  another.  By  such  prismatic  analysis  Dr. 
Draper  has  shown  that,  when  the  platinum  wire  first  begins 
to  glow,  the  light  emitted  is  a  pure  red.  As  the  glow 
augments  the  red  becomes  more  brilliant,  but  at  the  same 
time  orange  rays  are  added  to  the  emission.  Augmenting 
the  temperature  still  further,  yellow  rays  appear  beside  the 
orange,  after  the  yellow  green  rays  are  emitted,  and  after 
the  green  come,  in  succession,  blue,  indigo  and  violet  rays. 
To  display  all  these  colors  at  the  same  time  the  platinum 
wire  must  be  white-hot :  the  impression  of  whiteness  being 


RADIATION.  169 

in  fact  produced  by  the  simultaneous  action  of  all  these 
colors  on  the  optic  nerve. 

In  the  experiment  just  described  we  began  with  a  plat- 
inum wire  at  an  ordinary  temperature,  and  gradually 
raised  it  to  a  white  heat.  At  the  beginning,  and  even 
before  the  electric  current  had  acted  at  all  upon  the  wire, 
it  emitted  invisible  rays.  For  some  time  after  the  action 
of  the  current  had  commenced,  and  even  for  a  time  after 
the  wire  had  become  intolerable  to  the  touch,  its  radiation 
was  still  invisible.  The  question  now  arises,  what  becomes 
of  these  invisible  rays  when  the  visible  ones  make  their 
appearance?  It  will  be  proved  in  the  sequel  that  they 
maintain  themselves  in  the  radiation ;  that  a  ray  once 
emitted  continues  to  be  emitted  when  the  temperature 
is  increased,  and  hence  the  emission  from  our  platinum 
wire,  even  when  it  has  attained  its  maximum  brilliancy, 
consists  of  a  mixture  of  visible  and  invisible  rays.  If, 
instead  of  the  platinum  wire,  the  earth  itself  were  raised  to 
incandescence,  the  obscure  radiation  which  it  now  emits 
would  continue  to  be  emitted.  To  reach  incandescence  the 
planet  would  have  to  pass  through  all  the  stages  of  non- 
luminous  radiation,  and  the  final  emission  would  embrace 
the  rays  of  all  these  stages.  There  can  hardly  be  a  doubt 
that  from  the  sun  itself,  rays  proceed  similar  in  kind  to 
those  which  the  dark  earth  pours  nightly  into  space.  In 
fact,  the  various  kinds  of  obscure  rays  emitted  by  all  the 
planets  of  our  system  are  included  in  the  present  radiation 
of  the  sun. 

The  great  pioneer  in  this  domain  of  science  was  Sir 
William  Herschel.  Causing  a  beam  of  solar  light  to  pass 
through  a  prism  he  resolved  it  into  its  colored  constituents ; 
he  formed  what  is  technically  called  the  solar  spectrum. 
Exposing  thermometers  to  the  successive  colors  he  deter- 
mined their  heating  power,  and  found  it  to  augment  from 
the  violet  or  most  refracted  end,  to  the  red  or  least  refracted 
8 


170  FRAGMENTS  OF  SCIENCE. 

end  of  the  spectrum.  But  he  did  not  stop  here.  Pushing 
his  thermometers  into  the  dark  space  beyond  the  red  he 
found  that,  though  the  light  had  disappeared,  the  radiant 
heat  falling  on  the  instruments  was  more  intense  than  that 
at  any  visible  part  of  the  spectrum.  In  fact,  Sir  William 
Herschel  showed,  and  his  results  have  been  verified  by  vari- 
ous philosophers  since  his  time,  that  besides  its  luminous 
rays,  the  sun  pours  forth  a  multitude  of  other  rays  more 
powerfully  calorific  than  the  luminous  ones,  but  entirely 
unsuited  to  the  purposes  of  vision. 

At  the  less  refrangible  end  of  the  solar  spectrum,  then, 
the  range  of  the  sun's  radiation  is  not  limited  by  that  of 
the  eye.  The  same  statement  applies  to  the  more  refran- 
gible end.  Ritter  discovered  the  extension  of  the  spectrum 
into  the  invisible  region  beyond  the  violet ;  and,  in  recent 
times,  this  ultra-violet  emission  has  had  peculiar  interest 
conferred  upon  it  by  the  admirable  researches  of  Professor 
Stokes.  The  complete  spectrum  of  the  sun  consists,  there- 
fore, of  three  distinct  parts :  first,  of  ultra-red  rays  of  high 
heating  power,  but  unsuited  to  the  purposes  of  vision  ; 
secondly,  of  luminous  rays  which  display  the  succession  of 
colors,  red,  orange,  yellow,  green,  blue,  indigo,  violet; 
thirdly,  of  ultra-violet  rays  which,  like  the  ultra-red  ones, 
are  incompetent  to  excite  vision,  but  which,  unlike  the 
ultra-red  rays,  possess  a  very  feeble  heating  power.  In 
consequence,  however,  of  their  chemical  energy  these  ultra- 
violet rays  are  of  the  utmost  importance  to  the  organic 
world. 

2.    Origin  and  Character  of  Radiation.     The  Ether. 

"When  we  see  a  platinum  wire  raised  gradually  to  a 
white  heat,  and  emitting  in  succession  all  the  colors  of  the 
spectrum,  we  are  simply  conscious  of  a  series  of  changes  in 
the  condition  of  our  own  eyes.  We  do  not  see  the  actions 
in  which  these  successive  colors  originate,  but  the  mind 


EADIATION.  171 

irresistibly  infers  that  the  appearance  of  the  colors  corre- 
sponds to  certain  contemporaneous  changes  in  the  wire. 
What  is  the  nature  of  these  changes  ?  In  virtue  of  what 
condition  does  the  wire  radiate  at  all?  We  must  now 
look  from  the  wire  as  a  whole  to  its  constituent  atoms. 
Could  we  see  those  atoms,  even  before  the  electric  current 
has  begun  to  act  upon  them,  we  should  find  them  in  a 
state  of  vibration.  In  this  vibration,  indeed,  consists  such 
warmth  as  the  wire  then  possesses.  Locke  enunciated  this 
idea  with  great  precision,  and  it  seems  placed  beyond  the 
pale  of  doubt  by  the  excellent  quantitative  researches  of 
Mr.  Joule.  "Heat,"  says  Locke,  "is  a  very  brisk  agitation 
of  the  insensible  parts  of  the  object,  which  produce  in  us 
that  sensation  from  which  we  denominate  the  object  hot : 
so  what  in  our  sensation  is  heat  in  the  object  is  nothing 
but  motion"  When  the  electric  current,  still  feeble,  begins 
to  pass  through  the  wire,  its  first  act  is  to  intensify  the 
vibrations  already  existing,  by  causing  the  atoms  to  swing 
through  wider  ranges.  Technically  speaking,  the  ampli- 
tudes of  the  oscillations  are  increased.  The  current  does 
this,  however,  without  altering  the  periods  of  the  old  vi- 
brations, or  the  times  in  which  they  were  executed.  But 
besides  intensifying  the  old  vibrations  the  current  gener- 
ates new  and  more  rapid  ones,  and  when  a  certain  definite 
rapidity  has  been  attained  the  wire  begins  to  glow.  The 
color  first  exhibited  is  red,  which  corresponds  to  the  lowest 
rate  of  vibration  of  which  the  eye  is  able  to  take  cognizance. 
By  augmenting  the  strength  of  the  electric  current  more 
rapid  vibrations  are  introduced,  and  orange  rays  appear. 
A  quicker  rate  of  vibration  produces  yellow,  a  still  quicker 
green ;  and  by  further  augmenting  the  rapidity,  we  pass 
through  blue,  indigo,  and  violet,  to  the  extreme  ultra-violet 
rays. 

Such  are  the  changes  which  science  recognizes  in  the 
wire  itself,  as  concurrent  with  the  visual  changes  taking 


172  FRAGMENTS  OF  SCIENCE. 

place  in  the  eye.  But  what  connects  the  wire  with  this 
organ  ?  By  what  means  does  it  send  such  intelligence  of 
its  varying  condition  to  the  optic  nerve  ?  Heat  being,  as 
defined  by  Locke,  "  a  very  brisk  agitation  of  the  insensible 
parts  of  an  object,"  it  is  readily  conceivable  that  on  touch- 
ing a  heated  body  the  agitation  may  communicate  itself  to 
the  adjacent  nerves,  and  announce  itself  to  them  as  light 
or  heat.  But  the  optic  nerve  does  not  touch  the  hot  plati- 
num, and  hence  the  pertinence  of  the  question,  By  what 
agency  are  the  vibrations  of  the  wire  transmitted  to  the 
eye? 

The  answer  to  this  question  involves,  perhaps,  the  most 
important  physical  conception  that  the  mind  of  man  has 
yet  achieved :  the  conception  of  a  medium  filling  space  and 
fitted  mechanically  for  the  transmission  of  the  vibrations 
of  light  and  heat,  as  air  is  fitted  for  the  transmission  of 
sound.  This  medium  is  called  the  luminiferous  ether. 
Every  vibration  of  every  atom  of  our  platinum  wire  raises 
in  this  ether  a  wave,  which  speeds  through  it  at  the  rate 
of  186,000  miles  a  second.  The  ether  suffers  no  rupture 
of  continuity  at  the  surface  of  the  eye,  the  inter-molecular 
spaces  of  the  various  humors  are  filled  with  it ;  hence  the 
waves  generated  by  the  glowing  platinum  can  cross  these 
humors  and  impinge  on  the  optic  nerve  at  the  back  of  the 
eye.  Thus  the  sensation  of  light  reduces  itself  to  the  com- 
munication of  motion.  Up  to  this  point  we  deal  with  pure 
mechanics ;  but  the  subsequent  translation  of  the  shock  of 
the  ethereal  waves  into  consciousness  eludes  the  analysis 
of  science.  As  an  oar  dipping  into  the  Cam  generates 
systems  of  waves,  which,  speeding  from  the  centre  of  dis- 
turbance, finally  stir  the  sedges  on  the  river's  bank,  so  do 
the  vibrating  atoms  generate  in  the  surrounding  ether  un- 
dulations, which  finally  stir  the  filaments  of  the  retina. 
The  motion  thus  imparted  is  transmitted  with  measurable 
and  not  very  great  velocity  to  the  brain,  where,  by  a  pro- 


RADIATION.  173 

cess  which  science  does  not  even  tend  to  unravel,  the  tre- 
mor of  the  nervous  matter  is  converted  into  the  conscious 
impression  of  light. 

Darkness  might  then  be  defined  as  ether  at  rest ;  light 
as  ether  in  motion.  But  in  reality  the  ether  is  never  at 
rest,  for  in  the  absence  of  light-waves  we  have  heat-waves 
always  speeding  through  it.  In  the  spaces  of  the  universe 
both  classes  of  undulations  incessantly  commingle.  Here 
the  waves  issuing  from  uncounted  centres  cross,  coincide, 
oppose,  and  pass  through  each  other,  without  confusion  or 
ultimate  extinction.  The  waves  from  the  zenith  do  not 
jostle  out  of  existence  those  from  the  horizon,  and  every 
star  is  seen  across  the  entanglement  of  wave-motions  pro- 
duced by  all  other  stars.  It  is  the  ceaseless  thrill  which 
those  distant  orbs  collectively  create  in  the  ether,  which 
constitutes  what  we  call  the  temperature  of  space.  As  the 
air  of  a  room  accommodates  itself  to  the  requirements  of  an 
orchestra,  transmitting  each  vibration  of  every  pipe  and 
string,  so  does  the  inter-stellar  ether  accommodate  itself  to 
the  requirements  of  light  and  heat.  Its  waves  mingle  in 
space  without  disorder,  each  being  endowed  with  an  in- 
dividuality as  indestructible  as  if  it  alone  had  disturbed  the 
universal  repose. 

All  vagueness  with  regard  to  the  use  of  the  terms  radia- 
tion and  absorption  will  now  disappear.  Radiation  is  the 
communication  of  vibratory  motion  to  the  ether,  and  when 
a  body  is  said  to  be  chilled  by  radiation,  as  for  example  the 
grass  of  a  meadow  on  a  starlight  night,  the  meaning  is,  that 
the  molecules  of  the  grass  have  lost  a  portion  of  their  mo- 
tion, by  imparting  it  to  the  medium  in  which  they  vibrate. 
On  the  other  hand,  the  waves  of  ether  once  generated  may 
so  strike  against  the  molecules  of  a  body  exposed  to  their 
action  as  to  yield  up  their  motion  to  the  latter ;  and  in  this 
transfer  of  the  motion  from  the  ether  to  the  molecules  con- 
sists the  absorption  of  radiant  heat.  All  the  phenomena 


174  FRAGMENTS  OF  SCIENCE. 

of  heat  are  in  this  way  reducible  to  interchanges  of  motion ; 
and  it  is  purely  as  the  recipients  or  the  donors  of  this  mo- 
tion, that  we  ourselves  become  conscious  of  the  action  of 
heat  and  cold. 

3.   The  Atomic  Theory  in  reference  to  the  Ether. 

The  word  "  atoms  "  has  been  more  than  once  employed 
in  this  discourse.  Chemists  have  taught  us  that  all  matter 
is  reducible  to  certain  elementary  forms  to  which  they  give 
this  name.  These  atoms  are  endowed  with  powers  of 
mutual  attraction,  and  under  suitable  circumstances  they 
coalesce  to  form  compounds.  Thus  oxygen  and  hydrogen 
are  elements  when  separate,  or  merely  mixed,  but  they  may 
be  made  to  combine  so  as  to  form  molecules,  each  consisting 
of  two  atoms  of  hydrogen  and  one  of  oxygen.  In  this  con- 
dition they  constitute  water.  So  also  chlorine  and  sodium 
are  elements,  the  former  a  pungent  gas,  the  latter  a  soft 
metal ;  and  they  unite  together  to  form  chloride  of  sodium 
or  common  salt.  In  the  same  way  the  element  nitrogen 
combines  with  hydrogen,  in  the  proportion  of  one  atom  of 
the  former  to  three  of  the  latter,  to  form  ammonia  or  spirit 
of  hartshorn.  Picturing  in  imagination  the  atoms  of  ele- 
mentary bodies  as  little  spheres,  the  molecules  of  compound 
bodies  must  be  pictured  as  groups  of  such  spheres.  This  is 
the  atomic  theory  as  Dalton  conceived  it.  Now,  if  this 
theory  have  any  foundation  in  fact,  and  if  the  theory  of  an 
ether  pervading  space  and  constituting  the  vehicle  of  atomic 
motion  be  founded  in  fact,  we  may  assuredly  expect  the 
vibrations  of  elementary  bodies  to  be  profoundly  modified 
by  the  act  of  combination.  It  is  on  the  face  of  it  almost 
certain  that  both  as  regards  radiation  and  absorption,  that 
is  to  say,  both  as  regards  the  communication  of  motion  to 
the  ether  and  the  acceptance  of  motion  from  it,  the  deport- 
ment of  the  uncombined  will  be  different  from  that  of  the 
combined  atoms. 


RADIATION.  175 


4.  Absorption  of  Radiant  Heat  by  Gases. 

We  have  now  to  submit  these  considerations  to  the 
only  test  by  which  they  can  be  tried,  namely,  that  of  ex- 
periment. An  experiment  is  well  defined  as  a  question  put 
to  Nature ;  but  to  avoid  the  risk  of  asking  amiss  we  ought 
to  purify  the  question  from  all  adjuncts  which  do  not  neces- 
sarily belong  to  it.  Matter  has  been  shown  to  be  composed 
of  elementary  constituents,  by  the  compounding  of  which 
all  its  varieties  are  produced.  But  besides  the  chemical 
unions  which  they  form,  both  elementary  and  compound 
bodies  can  unite  in  another  and  less  intimate  way.  By  the 
attraction  of  cohesion  gases  and  vapors  aggregate  to  liquids 
and  solids,  without  any  change  of  their  chemical  nature. 
We  do  not  yet  know  how  the  transmission  of  radiant  heat 
may  be  affected  by  the  entanglement  due  to  cohesion,  and 
as  our  object  now  is  to  examine  the  influence  of  chemical 
union  alone,  we  shall  render  our  experiments  more  pure  by 
liberating  the  atoms  and  molecules  entirely  from  the  bonds 
of  cohesion,  and  employing  them  in  the  gaseous  or  vapor- 
ous form. 

Let  us  endeavor  to  obtain  a  perfectly  clear  mental  image 
of  the  problem  now  before  us.  Limiting  in  the  first  place 
our  inquiries  to  the  phenomena  of  absorption,  we  have  to 
picture  a  succession  of  waves  issuing  from  a  radiant  source 
and  passing  through  a  gas ;  some  of  them  striking  against 
the  gaseous  molecules  and  yielding  up  their  motion  to 
the  latter ;  others  gliding  round  the  molecules  or  passing 
through  the  inter-molecular  spaces  without  apparent  hinder- 
ance.  The  problem  before  us  is  to  determine  whether  such 
free  molecules  have  any  power  whatever  to  stop  the  waves 
of  heat,  and,  if  so,  whether  different  molecules  possess  this 
power  in  different  degrees. 

The  source   of  waves  which    I  shall  choose  for  these 


176  FRAGMENTS  OF  SCIENCE. 

experiments  is  a  plate  of  copper,  against  the  back  of  which 
a  steady  sheet  of  flame  is  permitted  to  play.  On  emerging 
from  the  copper,  the  waves,  in  the  first  instance,  pass 
through  a  space  devoid  of  air,  and  then  enter  a  hollow 
glass  cylinder,  three  feet  long  and  three  inches  wide.  The 
two  ends  of  this  cylinder  are  stopped  by  two  plates  of  rock- 
salt,  this  being  the  only  solid  substance  which  offers  a 
scarcely  sensible  obstacle  to  the  passage  of  the  calorific 
waves.  After  passing  through  the  tube,  the  radiant  heat 
falls  upon  the  anterior  face  of  a  thermo-electric  pile,1  which 
instantly  applies  the  heat  to  the  generation  of  an  electric 
current.  This  current  conducted  round  a  magnetic  needle 
deflects  it,  and  the  magnitude  of  the  deflection  is  a  measure 
of  the  heat  falling  upon  the  pile.  This  famous  instrument, 
and  not  an  ordinary  thermometer,  is  what  we  shall  use  in 
these  inquiries,  but  we  shall  use  it  in  a  somewhat  novel 
way.  As  long  as  the  two  opposite  faces  of  the  thermo- 
electric pile  are  kept  at  the  same  temperature,  no  matter 
how  high  that  may  be,  there  is  no  current  generated.  The 
current  is  a  consequence  of  the  difference  of  temperature 
between  the  two  opposite  faces  of  the  pile.  Hence,  if  after 
the  anterior  face  has  received  the  heat  from  our  radiating 
source,  a  second  source,  which  we  may  call  the  compensat- 
ing source,  be  permitted  to  radiate  against  the  posterior 
face,  this  latter  radiation  will  tend  to  neutralize  the  former. 
When  the  neutralization  is  perfect,  the  magnetic  needle 
connected  with  the  pile  is  no  longer  deflected,  but  points  to 
the  zero  of  the  graduated  circle  over  which  it  hangs. 

And  now  let  us  suppose  the  glass  tube,  through  which 
pass,  the  waves  from  the  heated  plate  of  copper,  to  be  ex- 
hausted by  an  air-pump,  the  two  sources  of  heat  acting  at 
the  same  time  on  the  two  opposite  faces  of  the  pile.  Per- 
fectly equal  quantities  of  heat  being  imparted  to  the  two 

1  In  the  Appendix  to  the  first  chapter  of  "  Heat  as  a  Mode  of  Motion," 
the  construction  of  the  thermo-electric  pile  is  fully  explained. 


RADIATION.  177 

faces,  the  needle  points  to  zero.  Let  any  gas  be  now  per- 
mitted to  enter  the  exhausted  tube  ;  if  the  molecules  pos- 
sess any  power  of  intercepting  the  calorific  waves,  the 
equilibrium  previously  existing  will  be  destroyed,  the  com- 
pensating source  will  triumph,  and  a  deflection  of  the  mag- 
netic needle  will  be  the  immediate  consequence.  From  the 
deflections  thus  produced  by  different  gases,  we  can  readily 
deduce  the  relative  amounts  of  wave-motion  which  their 
molecules  intercept. 

In  this  way  the  substances  mentioned  in  the  following 
table  were  examined,  a  small  portion  only  of  each  being 
admitted  into,  the  glass  tube.  The  quantity  admitted  was 
just  sufficient  to  depress  a  column  of  mercury  associated 
with  the  tube  one  inch  ;  in  other  words,  the  gases  were 
examined  at  a  pressure  of  one-thirtieth  of  an  atmosphere. 
The  numbers  in  the  table  express  the  relative  amounts  of 
wave-motion  absorbed  by  the  respective  gases,  the  quantity 
intercepted  by  atmospheric  air  being  taken  as  unity  : 

Radiation  through  Gases. 


Air  ......................................  1 

Oxygen  ..................................  1 

Nitrogen  .................................  1 

Hydrogen  ................................  1 

Carbonic  oxide  ...........................  750 

Carbonic  acid  ............................  972 

Hydrochloric  acid  .........................  1,005 

Nitric  oxide  ..............................  1,590 

Nitrous  oxide  .............................  1,860 

Sulphide  of  hydrogen  ......................  2,100 

Ammonia  ..........................  *.  ......  5,460 

Olefiant  gas  ..............................  6,030 

Sulphurous  acid  ...........................  6,480 

Every  gas  in  this  table  is  perfectly  transparent  to  light, 
that  is  to  say,  all  waves  within  the  limits  of  the  visible 


178  FRAGMENTS  OF  SCIENCE. 

spectrum  pass  through  it  without  obstruction  ;  but  for  the 
waves  of  slower  period,  emanating  from  our  heated  plate 
of  copper,  enormous  differences  of  absorptive  power  are 
manifested.  These  differences  illustrate  in  the  most  unex- 
pected manner  the  influence  of  chemical  combination.  Thus 
the  elementary  gases,  oxygen,  hydrogen,  and  nitrogen,  and 
the  mixture  atmospheric  air,  prove  to  be  practical  vacua  to 
the  rays  of  heat ;  for  every  ray,  or,  more  strictly  speaking, 
for  every  unit  of  wave-motion,  which  any  one  of  them  is 
competent  to  intercept,  perfectly  transparent  ammonia  in- 
tercepts 5,460  units,  defiant  gas  6,030  units,  while  sulphur- 
ous acid  gas  absorbs  6,480  units.  What  becomes  of  the 
wave-motion  thus  intercepted  ?  It  is  applied  to  the  heating 
of  the  absorbing  gas.  Through  air.  oxygen,  hydrogen,  and 
nitrogen,  on  the  contrary,  the  waves  of  ether  pass  without 
absorption,  and  these  gases  are  not  sensibly  changed  in 
temperature  by  the  most  powerful  calorific  rays.  The  po- 
sition of  nitrous  oxide  in  the  foregoing  table  is  worthy  of 
particular  notice.  In  this  gas  we  have  the  same  atoms,  in 
a  state  of  chemical  union,  that  exist  uncombined  in  the 
atmospheric  air;  but  the  absorption  of  the  compound  is 
1,800  times  that  of  air. 

5.  Formation  of  Invisible  Foci. 

This  extraordinary  deportment  of  the  elementary  gases 
naturally  directed  attention  to  elementary  bodies  in  another 
state  of  aggregation.  Some  of  Melloni's  results  now  at- 
tained a  new  significance ;  for  this  celebrated  experimenter 
had  found  crystals  of  the  element  sulphur  to  be  highly  per- 
vious to  radiant  heat ;  he  had  also  proved  that  lamp-black 
and  black  glass  (which  owes  its  blackness  to  the  element 
carbon)  were  to  considerable  extent  transparent  to  calorific 
rays  of  low  refrangibility.  These  facts,  harmonizing  so 
strikingly  with  the  deportment  of  the  simple  gases,  sug- 


RADIATION.  179 

gested  further  inquiry.  Sulphur  dissolved  in  bisulphate  of 
carbon  was  found  almost  perfectly  transparent.  The  dense 
and  deeply-colored  element  bromine  was  examined,  and 
found  competent  to  cut  off  the  light  of  our  most  brilliant 
flames,  while  it  transmitted  the  invisible  calorific  rays  with 
extreme  freedom.  Iodine,  the  companion-element  of  bro- 
mine, was  next  thought  of,  but  it  was  found  impracticable 
to  examine  the  substance  in  its  usual  solid  condition.  It 
however  dissolves  freely  in  bisulphide  of  carbon.  There  is 
no  chemical  union  between  the  liquid  and  the  iodine ;  it  is 
simply  a  case  of  solution,  in  which  the  uncombined  atoms 
of  the  element  can  act  upon  the  radiant  heat.  When  per- 
mitted to  do  so,  it  was  found  that  a  layer  of  dissolved 
iodine,  sufficiently  opaque  to  cut  off  the  light  of  the  mid- 
day sun,  was  almost  absolutely  transparent  to  the  invisible 
calorific  rays. 

By  prismatic  analysis  Sir  William  Herschel  separated 
the  luminous  from  the  non-luminous  rays  of  the  sun,  and 
he  also  sought  to  render  the  obscure  rays  visible  by  con- 
centration. Intercepting  the  luminous  portion  of  his  spec- 
trum he  brought,  by  a  converging  lens,  the  ultra-red  rays 
to  a  focus,  but  by  this  condensation  he  obtained  no  light. 
The  solution  of  iodine  offers  a  means  of  filtering  the  solar 
beam,  or,  failing  it,  the  beam  of  the  electric  lamp,  which 
renders  attainable  far  more  powerful  foci  of  invisible  rays 
than  could  possibly  be  obtained  by  the  method  of  Sir  Wil- 
liam Herschel.  For  to  form  his  spectrum  he  was  obliged 
to  operate  upon  solar  light  which  had  passed  through 
a  narrow  slit  or  through  a  small  aperture,  the  amount  of 
the  obscure  heat  being  limited  by  this  circumstance.  But 
with  our  opaque  solution  we  may  employ  the  entire  surface 
of  the  largest  lens,  and  having  thus  converged  the  rays, 
luminous  and  non-luminous,  we  can  intercept  the  former  by 
the  iodine,  and  do  what  wre  please  with  the  latter.  Ex- 
periments of  this  character,  not  only  with  the  iodine  solu- 


180  FRAGMENTS  OF  SCIENCE. 

tion,  but  also  with  black  glass  and  layers  of  lamp-black, 
were  publicly  performed  at  the  Royal  Institution  in  the 
early  part  of  1862,  and  the  effects  at  the  foci  of  invisible 
rays  then  obtained  were  such  as  had  never  been  witnessed 
previously. 

In  the  experiments  here  referred  to,  glass  lenses  were 
employed  to  concentrate  the  rays.  But  glass,  though 
highly  transparent  to  the  luminous,  is  in  a  high  degree 
opaque  to  the  invisible  heat-rays  of  the  electric  lamp,  and 
hence  a  large  portion  of  those  rays  was  intercepted  by  the 
glass.  The  obvious  remedy  here  is  to  employ  rock-salt 
lenses  instead  of  glass  ones,  or  to  abandon  the  use  of  lenses 
wholly,  and  to  concentrate  the  rays  by  a  metallic  mirror. 
Both  of  these  improvements  have  been  introduced,  and,  as 
anticipated,  the  invisible  foci  have  been  thereby  rendered 
more  intense.  The  mode  of  operating  remains,  however,  the 
same,  in  principle,  as  that  made  known  in  1862.  It  was 
then  found  that  an  instant's  exposure  of  the  face  of  the 
thermo-electric  pile  to  the  focus  of  invisible  rays,  dashed 
the  needles  of  a  coarse  galvanometer  violently  aside.  It  is 
now  found  that  on  substituting  for  the  face  of  the  thermo- 
electric pile  a  combustible  body,  the  invisible  rays  are 
competent  to  set  that  body  on  fire. 

6.    Visible  and  Invisible  J%ays  of  the  Electric  Light. 

We  have  next  to  examine  what  proportion  the  non 
luminous  rays  of  the  electric  light  bear  to  the  luminous 
ones.  This  the  opaque  solution  of  iodine  enables  us  to  do 
with  an  extremely  close  approximation  to  the  truth.  The 
pure  bisulphide  of  carbon,  which  is  the  solvent  of  the 
iodine,  is  perfectly  transparent  to  the  luminous,  and  almost 
perfectly  transparent  to  the  dark  rays  of  the  electric  lamp. 
Through  the  transparent  bisulphide  the  total  radiation  of 
the  lamp  may  be  considered  to  pass,  while  through  the 


RADIATION.  181 

solution  of  iodine  only  the  dark  rays  are  transmitted. 
Determining,  then,  by  means  of  a  thermo-electric  pile,  the 
total  radiation,  and  deducting  from  it  the  purely  obscure, 
we  obtain  the  amount  of  the  purely  luminous  emission. 
Experiments,  performed  in  this  way,  prove  that  if  all  the 
visible  rays  of  the  electric  light  were  converged  to  a  focus 
of  dazzling  brilliancy,  its  heat  would  only  be  one-ninth  of 
that  produced  at  the  unseen  focus  of  the  invisible  rays. 

Exposing  his  thermometers  to  the  successive  colors  of 
the  solar  spectrum,  Sir  William  Herschel  determined  the 
heating  power  of  each,  and  also  that  of  the  region  beyond 
the  extreme  red.  Then  drawing  a  straight  line  to  represent 
the  length  of  the  spectrum,  he  erected,  at  various  points, 
perpendiculars  to  represent  the  calorific  intensity  existing 
at  those  points.  Uniting  the  ends  of  all  his  perpendiculars, 
he  obtained  a  curve  which  showed  at  a  glance  the  manner 
in  which  the  heat  was  distributed  in  the  solar  spectrum. 
Professor  Mliller,  of  Freiburg,  with  improved  instruments, 
afterward  made  similar  experiments,  and  constructed  a 
more  accurate  diagram  of  the  same  kind.  We  have  now  to 
examine  the  distribution  of  heat  in  the  spectrum  of  the 
electric  light ;  and  for  this  purpose  we  shall  employ  a  par- 
ticular form  of  the  thermo-electric  pile,  devised  by  Melloni. 
Its  face  is  a  rectangle,  which  by  means  of  movable  side- 
pieces  can  be  rendered  as  narrow  as  desired.  We  can,  for 
example,  have  the  face  of  the  pile  the  tenth,  the  hundredth, 
or  even  the  thousandth  of  an  inch  in  breadth.  By  means 
of  an  endless  screw,  this  linear  thermo-electric  pile  may  be 
moved  through  the  entire  spectrum,  from  the  violet  to  the 
red,  the  amount  of  heat  falling  upon  the  pile  at  every  point 
of  its  march,  being  declared  by  a  magnetic  needle  associated 
with  the  pile. 

When  this  instrument  is  brought  up  to  the  violet  end  of 
the  spectrum  of  the  electric  light,  the  heat  is  found  to  be 
insensible.  As  the  pile  gradually  moves  from  the  violet 


182  FRAGMENTS  OF  SCIENCE. 

end  toward  the  red,  heat  soon  manifests  itself,  augmenting 
as  we  approach  the  red.  Of  all  the  colors  of  the  visible 
spectrum  the  red  possesses  the  highest  heating  power.  On 
pushing  the  pile  into  the  dark  region  beyond  the  red,  the 
heat,  instead  of  vanishing,  rises  suddenly  and  enormously 
in  intensity,  until  at  some  distance  beyond  the  red  it 
attains  a  maximum.  Moving  the  pile  still  forward,  the 
thermal  power  falls,  somewhat  more  rapidly  than  it  rose. 
It  then  gradually  shades  away,  but  for  a  distance  beyond 
the  red  greater  than  the  length  of  the  whole  visible  spec- 
trum, signs  of  heat  may  be  detected.  Drawing  a  datum 
line,  and  erecting  along  it  perpendiculars,  proportional  in 
length  to  the  thermal  intensity  at  the  respective  points,  we 
obtain  the  extraordinary  curve,  shown  on  the  adjacent  page, 
which  exhibits  the  distribution  of  heat  in  the  spectrum  of 
the  electric  light.  In  the  region  of  dark  rays,  beyond  the 
red,  the  curve  shoots  up  to  B,  in  a  steep  and  massive  peak 
— a  kind  of  Matterhorn  of  heat,  which  dwarfs  the  portion 
of  the  diagram  C  D  E,  representing  the  luminous  radiation. 
Indeed,  the  idea  forced  upon  the  mind  by  this  diagram  is 
that  the  light-rays  are  a  mere  insignificant  appendage  to 
the  heat-rays  represented  by  the  area  A  B  C  D,  thrown  in 
as  it  were  by  Nature  for  the  purposes  of  vision. 

The  diagram  drawn  by  Professor  Mliller  to  represent 
the  distribution  of  heat  in  the  solar  spectrum  is  not  by  any 
means  so  striking  as  that  just  described,  and  the  reason, 
doubtless,  is  that  prior  to  reaching  the  earth  the  solar  rays 
have  to  traverse  our  atmosphere.  By  the  aqueous  vapor 
there  diffused,  the  summit  of  the  peak  representing  the 
sun's  invisible 'radiation  is  cut  off.  A  similar  lowering  of 
the  mountain  of  invisible  heat  is  observed  when  the  rays 
from  the  electric  light  are  permitted  to  pass  through  a  film 
of  water,  which  acts  upon  them  as  the  atmospheric  vapor 
acts  upon  the  rays  of  the  sun. 


184  FRAGMENTS  OF  SCIENCE. 

7.    Combustion  by  Invisible  Mays. 

The  sun's  invisible  rays  far  transcend  the  visible  ones 
in  heating  power,  so  that  if  the  alleged  performances  of 
Archimedes  during  the  siege  of  Syracuse  had  any  founda- 
tion in  fact,  the  dark  solar  rays  would  have  been  the  phi- 
losopher's chief  agents  of  combustion.  On  a  small  scale 
we  can  readily  produce  with  the  purely  invisible  rays  of 
the  electric  light  all  that  Archimedes  is  said  to  have  per- 
formed with  the  sun's  total  radiation.  Placing  behind  the 
electric  light  a  small  concave  mirror,  the  rays  are  converged, 
the  cone  of  reflected  rays  and  their  point  of  convergence 
being  rendered  clearly  visible  by  the  dust  always  floating 
in  the  air.  Placing,  between  the  luminous  focus  and  the 
source  of  rays,  our  solution  of  iodine,  the  light  of  the  cone 
is  entirely  cut  away,  but  the  intolerable  heat  experienced 
when  the  hand  is  placed,  even  for  a  moment,  at  the  dark 
focus,  shows  that  the  calorific  rays  pass  unimpeded  through 
the  opaque  solution. 

Almost  any  thing  that  ordinary  fire  can  effect  may  be 
accomplished  at  the  focus  of  invisible  rays ;  the  air  at  the 
focus  remaining  at  the  same  time  perfectly  cold,  on  ac- 
count of  its  transparency  to  the  heat-rays.  An  air-ther- 
mometer, with  a  hollow  rock-salt  bulb,  would  be  unaffected 
by  the  heat  of  the  focus :  there  would  be  no  expansion, 
and  in  the  open  air  there  is  no  convection.  The  ether  at 
the  focus,  and  not  the  air,  is  the  substance  in  which  the 
heat  is  embodied.  A  block  of  wood,  placed  at  the  focus, 
absorbs  the  heat,  and  dense  volumes  of  smoke  rise  swiftly 
upward,  showing  the  manner  in  which  the  air  itself  would 
rise,  if  the  invisible  rays  were  competent  to  heat  it.  At 
the  perfectly  dark  focus  dry  paper  is  instantly  inflamed : 
chips  of  wood  are  speedily  burnt  up :  lead,  tin,  and  zinc, 
are  fused :  and  disks  of  charred  paper  are  raised  to  vivid 
incandescence.  It  might  be  supposed  that  the  obscure  rays 


RADIATION.  185 

would  show  no  preference  for  black  over  white ;  but  they 
do  show  a  preference,  and,  to  obtain  rapid  combustion,  the 
body,  if  not  already  black,  ought  to  be  blackened.  When 
metals  are  to  be  burned,  it  is  necessary  to  blacken  or 
otherwise  tarnish  them,  so  as  to  diminish  their  reflective 
power.  Blackened  zinc-foil,  when  brought  into  the  focus 
of  invisible  rays,  is  instantly  caused  to  blaze,  and  burns 
with  its  peculiar  purple  flame.  Magnesium  wire  flattened, 
or  tarnished  magnesium  ribbon,  also  bursts  into  splendid 
combustion.  Pieces  of  charcoal  suspended  in  a  receiver 
full  of  oxygen  are  also  set  on  fire :  the  dark  rays  after  hav- 
ing passed  through  the  receiver  still  possessing  sufficient 
power  to  ignite  the  charcoal,  and  thus  initiate  the  attack 
of  the  oxygen.  If,  instead  of  being  plunged  in  oxygen, 
the  charcoal  be  suspended  in  vacuo,  it  immediately  glows 
at  the  place  where  the  focus  falls. 

8.  Transmutation  of  Rays : 1    Calorescence. 

Eminent  experimenters  were  long  occupied  in  demon- 
strating the  substantial  identity  of  light  and  radiant  heat, 
and  we  have  now  the  means  of  offering  a  new  and  striking 
proof  of  this  identity.  A  concave  mirror  produces  beyond 
the  object  which  it  reflects  an  inverted  and  magnified  image 
of  the  object ;  withdrawing,  for  example,  our  iodine  solu- 
tion, an  intensely  luminous  inverted  image  of  the  carbon 
points  of  the  electric  light  is  formed  at  the  focus  of  the 
mirror  employed  in  the  foregoing  experiments.  When  the 
solution  is  interposed,  and  the  light  is  cut  away,  what 
becomes  of  this  image  ?  It  disappears  from  sight,  but  an 
invisible  thermograph  remains,  and  it  is  only  the  peculiar 
constitution  of  our  eyes  that  disqualifies  us  from  seeing 
the  picture  formed  by  the  calorific  rays.  Falling  on 
white  paper,  the  image  chars  itself  out :  falling  on  black 

1  I  borrow  this  term  from  Professor  Challis,  "  Philosophical  Maga- 
zine," vol.  xii.,  p.  521. 


186  FRAGMENTS  OF  SCIENCE. 

paper,  two  holes  are  pierced  in  it,  corresponding  to  the 
images  of  the  two  coal  points  :  but  falling  on  a  thin  plate 
of  carbon  in  vacuo,  or  upon  a  thin  sheet  of  platinized  plat- 
inum, either  in  vacuo  or  in  air,  radiant  heat  is  converted 
into  light,  and  the  image  stamps  itself  in  vivid  incandes- 
cence upon  both  the  carbon  and  the  metal.  Results  similar  to 
those  obtained  with  the  electric  light  have  also  been  obtained 
with  the  invisible  rays  of  the  lime-light  and  of  the  sun. 

Before  a  Cambridge  audience  it  is  hardly  necessary  to 
refer  to  the  excellent  researches  of  Professor  Stokes  at 
the  opposite  end  of  the  spectrum.  The  above  results  con- 
stitute a  kind  of  complement  to  his  discoveries.  Professor 
Stokes  named  the  phenomena  which  he  has  discovered  and 
investigated  Fluorescence  •  for  the  new  phenomena  here 
described  I  have  proposed  the  term  Calorescence.  He,  by 
the  interposition  of  a  proper  medium,  so  lowered  the  re- 
frangibility  of  the  ultra-violet  rays  of  the  spectrum  as  to 
render  them  visible ;  and  here,  by  the  interposition  of  the 
platinum-foil,  the  refrangibility  of  the  ultra-red  rays  is  so 
exalted  as  to  render  them  visible.  Looking  through  a 
prism  at  the  incandescent  image  of  the  carbon  points,  the 
light  of  the  image  is  decomposed,  and  a  complete  spectrum 
obtained.  The  invisible  rays  of  the  electric  light,  remoulded 
by  the  atoms  of  the  platinum,  shine  thus  visibly  forth ;  ultra- 
red  rays  being  converted  into  red,  orange,  yellow,  green, 
blue,  indigo,  and  ultra-violet  ones.  Could  we,  moreover, 
raise  the  original  source  of  rays  to  a  sufficiently  high  tem- 
perature, we  might  not  only  obtain  from  the  dark  rays  of 
such  a  source  a  single  incandescent  image,  but  from  the 
dark  rays  of  this  image  we  might  obtain  a  second  one,  from 
the  dark  rays  of  the  second  a  third,  and  so  on — a  series  of 
complete  images  and  spectra  being  thus  extracted  from  the 
invisible  emission  of  the  primitive  source.1 

1  On  investigating  the  calorescence  produced  by  rays  transmitted 
through  glasses  of  various  colors,  it  was  found  that  in  the  case  of  certain 


RADIATION.  187 


9.  Deadness  of  the  Optic  Nerve  to  the  Calorific  JRays. 

The  layer  of  iodine  used  in  the  foregoing  experiments 
intercepted  the  light  of  the  noonday  sun.  No  trace  of 
light  from  the  electric  lamp  was  visible  in  the  darkest 
room,  even  when  a  white  screen  was  placed  at  the  focus  of 
the  mirror  employed  to  concentrate  the  light.  It  was 
thought,  however,  that  if  the  retina  itself  were  brought 
into  the  focus  the  sensation  of  light  might  be  experienced. 
The  danger  of  this  experiment  was  twofold.  If  the  dark 
rays  were  absorbed  in  a  high  degree  by  the  humors  of  the 
eye,  the  albumen  of  the  humors  might  coagulate  along  the 
line  of  the  rays.  If,  on  the  contrary,  no  such  high  ab- 
sorption took  place,  the  rays  might  reach  the  retina  with  a 
force  sufficient  to  destroy  it.  To  test  the  likelihood  of  these 
results,  experiments  were  made  on  water  and  on  a  solution  of 
alum,  and  they  showed  it  to  be  very  improbable  that  in  the 
brief  time  requisite  for  an  experiment  any  serious  damage 

specimens  of  blue  glass,  the  platinum-foil  glowed  with  a  pink  or  purplish 
light.  The  effect  was  not  subjective,  and  considerations  of  obvious  in- 
terest are  suggested  by  it.  Different  kinds  of  black  glass  differ  notably 
as  to  their  power  of  transmitting  radiant  heat.  In  thin  plates  some  de- 
scriptions tint  the  sun  with  a  greenish  hue :  others  make  it  appear  a 
glowing  red  without  any  trace  of  green.  The  latter  are  far  more  diather- 
mic than  the  former.  In  fact,  carbon  when  perfectly  dissolved,  and  in- 
corporated with  a  good  white  glass,  is  highly  transparent  to  the  calorific 
rays,  and  by  employing  it  as  an  absorbent,  the  phenomena  of  "  calores- 
cence  "  may  be  obtained,  though  in  a  less  striking  form  than  with  the 
iodine.  The  black  glass  chosen  for  thermometers,  and  intended  to  ab- 
sorb completely  the  solar  heat,  may  entirely  fail  in  this  object,  if  the 
glass  in  which  the  carbon  is  incorporated  be  colorless.  To  render  the 
bulb  of  a  thermometer  a  perfect  absorbent,  the  glass  ought  in  the  first 
instance  to  be  green.  Soon  after  the  discovery  of  fluorescence  the  late 
Dr.  William  Allen  Miller  pointed  to  the  lime-light  as  an  illustration  of 
exalted  refrangibility.  Direct  experiments  have  since  entirely  confirmed 
the  view  expressed  at  page  210  of  his  work  on  "  Chemistry,"  published 
in  1855. 


188  FRAGMENTS  OF  SCIENCE. 

could  be  done.  The  eye  was  therefore  caused  to  approach 
the  dark  focus,  no  defence,  in  the  first  instance,  being  pro- 
vided ;  but  the  heat,  acting  upon  the  parts  surrounding  the 
pupil,  could  not  be  borne.  An  aperture  was,  therefore, 
pierced  in  a  plate  of  metal,  and  the  eye  placed  behind  the 
aperture,  was  caused  to  approach  the  point  of  convergence 
of  invisible  rays.  The  focus  was  attained,  first  by  the 
pupil  and  afterward  by  the  retina.  Removing  the  eye,  but 
permitting  the  plate  of  metal  to  remain,  a  sheet  of  platinum- 
foil  was  placed  in  the  position  occupied  by  the  retina  a  mo- 
ment before.  The  platinum  became  red  hot.  No  sensible 
damage  was  done  to  the  eye  by  this  experiment ;  no  im- 
pression of  light  was  produced;  the  optic  nerve  was  not 
even  conscious  of  heat. 

But  the  humors  of  the  eye  are  known  to  be  highly  im- 
pervious to  the  invisible  calorific  rays,  and  the  question 
therefore  arises,  "  Did  the  radiation  in  the  foregoing  experi- 
ment reach  the  retina  at  all  ? "  The  answer  is,  that  the 
rays  were  in  part  transmitted  to  the  retina,  and  in  part  ab- 
sorbed by  the  humors.  Experiments  on  the  eye  of  an  ox 
showed  that  the  proportion  of  obscure  rays  which  reached 
the  retina  amounted  to  18  per  cent,  of  the  total  radiation ; 
while  the  luminous  emission  from  the  electric  light  amounts 
to  no  more  than  10  per  cent,  of  the  same  total.  Were  the 
purely  luminous  rays  of  the  electric  lamp  converged  by  our 
mirror  to  a  focus,  there  can  be  no  doubt  as  to  the  fate  of  a 
retina  placed  there.  Its  ruin  would  be  inevitable ;  and  yet 
this  would  be  accomplished  by  an  amount  of  wave-motion 
but  little  more  than  half  of  that  which  the  retina  bears, 
without  exciting  consciousness,  at  the  focus  of  invisible 
rays. 

This  subject  will  repay  a  moment's  further  attention. 
At  a  common  distance  of  a  foot  the  visible  radiation  of  the 
electric  light  is  800  times  the  light  of  a  candle.  At  the 
same  distance,  the  portion  of  the  radiation  of  the  electric 


RADIATION.  189 

light  which  reaches  the  retina  but  fails  to  excite  vision,  is 
about  1,500  times  the  luminous  radiation  of  the  candle.1 
But  a  candle  on  a  clear  night  can  readily  be  seen  at  a  dis- 
tance of  a  mile,  its  light  at  this  distance  being  less  than 
one  20,000,000th  of  its  light  at  the  distance  of  a  foot. 
Hence,  to  make  the  candle-light  a  mile  off  equal  in  power 
to  the  non-luminous  radiation  received  from  the  electric 
light  at  a  foot  distance,  its  intensity  would  have  to  be  mul- 
tiplied by  1,500  X  20,000,000,  or  by  thirty  thousand  mill- 
ions. Thus  the  thirty  thousand  millionth  part  of  the  in- 
visible radiation  from  the  electric  light,  received  by  the 
retina  at  the  distance  of  a  foot,  would,  if  slightly  changed 
in  character,  be  amply  sufficient  to  provoke  vision.  Nothing 
could  more  forcibly  illustrate  that  special  relationship  sup- 
posed by  Melloni  and  others  to  subsist  between  the  optic 
nerve  and  the  oscillating  periods  of  luminous  bodies.  The 
optic  nerve  responds,  as  it  were,  to  the  waves  with  which 
it  is  in  consonance,  while  it  refuses  to  be  excited  by  others 
of  almost  infinitely  greater  energy,  whose  periods  of  recur- 
rence are  not  in  unison  with  its  own. 

10.  Persistence  of  Hays. 

At  an  early  part  of  this  lecture  it  was  affirmed  that 
when  a  platinum  wire  was  gradually  raised  to  a  state  of 
high  incandescence,  new  rays  were  constantly  added, 
while  the  intensity  of  the  old  ones  was  increased.  Thus 
in  Dr.  Draper's  experiments  the  rise  of  temperature  that 
generated  the  orange,  yellow,  green,  and  blue  rays,  aug- 
mented the  intensity  of  the  red  ones.  What  is  true  of  the 
red  is  true  of  every  other  ray  of  the  spectrum,  visible  and 
invisible.  We  cannot  indeed  see  the  augmentation  of  in- 

1  It  will  be  borne  in  mind  that  the  heat  which  any  ray,  luminous  or 
non-luminous,  is  competent  to  generate  is  the  true  measure  of  the  energy 
of  the  ray. 


190  '  FRAGMENTS  OF  SCIENCE. 

tensity  in  the  region  beyond  the  red,  but  we  can  measure 
it  and  express  it  numerically.  With  this  view  the  following 
experiment  was  performed.  A  spiral  of  platinum  wire  was 
surrounded  by  a  small  glass  globe  to  protect  it  from  cur- 
rents of  air ;  through  an  orifice  in  the  globe  the  rays  could 
pass  from  the  spiral  and  fall  afterward  upon  a  thermo-elec- 
tric pile.  Placing  in  front  of  the  orifice  an  opaque  solution 
of  iodine,  the  platinum  was  gradually  raised  from  a  low 
dark  heat  to  the  fullest  incandescence,  with  the  following 
results : 

Appearance  Energy  of 

of  spiral.  obscure  radiation. 

Dark 1 

Dark,  but  hotter 3 

Dark,  but  still  hotter 5 

Dark,  but  still  hotter 10 

Feeble  red 19 

Dull  red 25 

Red 37 

Full  red 62 

Orange 89 

Bright  orange 144 

Yellow 202 

White 276 

Intense  white 440 

Thus  the  augmentation  of  the  electric  current,  which 
raises  the  wire  from  its  primitive  dark  condition  to  an  in- 
tense white  heat,  exalts  at  the  same  time  the  energy  of  the 
obscure  radiation,  until  at  the  end  it  is  fully  four  hundred 
and  forty  times  what  it  was  at  the  beginning. 

What  has  been  here  proved  true  of  the  totality  of  the 
ultra-red  rays  is  true  for  each  of  them  singly.  Placing  our 
linear  thermo-electric  pile  in  any  part  of  the  ultra-red  spec- 
trum, it  may  be  proved  that  a  ray  once  emitted  continues 
to  be  emitted  with  increased  energy  as  the  temperature  is 
augmented.  The  platinum  spiral  so  often  referred  to  being 


RADIATION.  191 

raised  to  whiteness  by  an  electric  current,  a  brilliant  spec- 
trum was  formed  from  its  light.  A  linear  thermo-electric 
pile  was  placed  in  the  region  of  obscure  rays  beyond  the 
red,  and  by  diminishing  the  current  the  spiral  was  reduced 
to  a  low  temperature.  It  was  then  caused  to  pass  through 
various  degrees  of  darkness  and  incandescence,  with  the 
following  results : 

Appearance  Energy  of 

of  spiral  obscure  rays. 

Dark 1 

Dark 6 

Faint  red 10 

Dull  red 13 

Red 18 

Full  red ' 27 

Orange 60 

Yellow 93 

White 122 

Here,  as  in  the  former  case,  the  dark  and  bright  radia- 
tions reached  their  maximum  together;  as  the  one  aug- 
mented, the  other  augmented,  until  at  last  the  energy  of 
the  obscure  rays  of  the  particular  refrangibility  here  chosen, 
became  one  hundred  and  twenty-two  times  what  it  was  at 
first.  To  reach  a  white  heat  the  wire  has  to  pass  through 
all  the  stages  of  invisible  radiation,  and  in  its  most  brilliant 
condition  it  embraces,  in  an  intensified  form,  the  rays  of  all 
those  stages. 

And  thus  it  is  with  all  other  kinds  of  matter,  as  far  as 
they  have  hitherto  been  examined.  Coke,  whether  brought 
to  a  white  heat  by  the  electric  current,  or  by  the  oxyhydro- 
gen  jet,  pours  out  invisible  rays  with  augmented  energy, 
as  its  light  is  increased.  The  same  is  true  of  lime,  bricks, 
and  other  substances.  It  is  true  of  all  metals  which  are 
capable  of  being  heated  to  incandescence.  It  also  holds 
good  for  phosphorus  burning  in  oxygen.  Every  gush  of 
dazzling  light  has  associated  with  it  a  gush  of  invisible  ra- 


192  FRAGMENTS  OF  SCIENCE. 

diant  heat,  which  far  transcends  the  light  in  energy.  This 
condition  of  things  applies  to  all  bodies  capable  of  being- 
raised  to  a  white  heat,  either  in  the  solid  or  the  molten 
condition.  It  would  doubtless  also  apply  to  the  luminous 
fogs  formed  by  the  condensation  of  incandescent  vapors. 
In  such  cases  when  the  curve  representing  the  radiant  en- 
ergy of  the  body  is  constructed,  the  obscure  radiation  tow- 
ers upward  like  a  mountain,  the  luminous  radiation  resem- 
bling a  mere  spur  at  its  base.  From  the  very  brightness 
of  the  light  of  some  of  the  fixed  stars  we  may  infer  the 
intensity  of  the  dark  radiation,  which  is  the  precursor  and 
inseparable  associate  of  their  luminous  rays. 

We  thus  find  the  luminous  radiation  appearing  when 
the  radiant  body  has  attained  a  certain  temperature ;  or, 
in  other  words,  when  the  vibrating  atoms  of  the  body  have 
attained  a  certain  width  of  swing.  In  solid  and  molten 
bodies  a  certain  amplitude  cannot  be  surpassed  without 
the  introduction  of  periods  of  vibration,  which  provoke 
the  sense  of  vision.  How  are  we  to  figure  this  ?  If  per- 
mitted to  speculate,  we  might  ask,  Are  not  these  more 
rapid  vibrations  the  progeny  of  the  slower  ?  Is  it  not  really 
the  mutual  action  of  the  atoms,  when  they  swing  through 
very  wide  spaces,  and  thus  encroach  upon  each  other,  that 
causes  them  to  tremble  in  quicker  periods  ?  If  so,  what- 
ever be  the  agency  by  which  the  large  swinging  space  is 
obtained,  we  shall  have  light-giving  vibrations  associated 
with  it.  It  matters  not  whether  the  large  amplitudes  be 
produced  by  the  strokes  of  a  hammer,  or  by  the  blows  of 
the  molecules  of  a  non-luminous  gas,  such  as  the  air  at  some 
height  above  a  gas-flame ;  or  by  the  shock  of  the  ether- 
particles  when  transmitting  radiant  heat.  The  result  in 
all  cases  will  be  incandescence.  Thus,  the  invisible  waves 
of  our  filtered  electric  beam  may  be  regarded  as  generating 
synchronous  vibrations  among  the  atoms  of  the  platinum 
on  which  they  impinge ;  but  once  these  vibrations  have  at- 


RADIATION.  193 

tained  a  certain  amplitude,  the  mutual  jostling  of  the  atoms 
produces  quicker  tremors,  and  the  light-giving  waves  fol- 
low as  the  necessary  product  of  the  heat-giving  ones. 

11.   Absorption  of  Radiant  Heat  l>y  Vapors 
and  Odors. 

We  commenced  the  demonstrations  brought  forward  in 
this  lecture  by  experiments  on  permanent  gases,  and  we 
have  now  to  turn  our  attention  to  the  vapors  of  volatile 
liquids.  Here,  as  in  the  case  .of  the  gases,  vast  differences 
have  been  proved  to  exist  between  various  kinds  of  mole- 
cules, as  regards  their  power  of  intercepting  the  calorific 
waves.  While  some  vapors  allow  the  waves  a  compara- 
tively free  passage,  the  minutest  bubble  of  other  vapors, 
introduced  into  the  tube  already  employed  for  gases,  causes 
a  deflection  of  the  magnetic  needle.  Assuming  the  ab- 
sorption effected  by  air  at  a  pressure  of  one  atmosphere  to 
be  unity,  the  followng  are  the  absorptions  effected  by  a  se- 
.ries  of  vapors  at  a  pressure  of  one-sixtieth  of  an  atmos- 
phere : 

Name  of  vapor.  Absorption. 

Bisulphide  of  carbon 47 

Iodide  of  methyl 115 

Benzol 136 

Amylene 321 

Sulphuric  ether 440 

Formic  ether 548 

Acetic  ether 612 

Bisulphide  of  carbon  is  the  most  transparent  vapor  in 
this  list ;  and  acetic  ether  the  most  opaque ;  one-sixtieth 
of  an  atmosphere  of  the  former,  however,  produces  forty- 
seven  times  the  effect  of  a  whole  atmosphere  of  air,  while 
one-sixtieth  of  an  atmosphere  of  the  latter  produces  six 
hundred  and  twelve  times  the  effect  of  a  whole  atmos- 
phere of  air.  Reducing  dry  air  to  the  pressure  of  the  acetic 
9 


194  FRAGMENTS  OF  SCIENCE. 

ether  here  employed,  and  comparing  them  then  together, 
the  quantity  of  wave-motion  intercepted  by  the  ether  would 
be  many  thousand  times  that  intercepted  by  the  air. 

Any  one  of  these  vapors  discharged  into  the  free  atmos- 
phere, in  front  of  a  body  emitting  obscure  rays,  intercepts 
more  or  less  of  the  radiation.  A  similar  effect  is  produced 
by  perfumes  diffused  in  the  air,  though  their  attenuation  is 
known  to  be  almost  infinite.  Carrying,  for  example,  a  cur- 
rent of  dry  air  over  bibulous  paper  moistened  by  patchouli, 
the  scent  taken  up  by  the  current  absorbs  30  times  the 
quantity  of  heat  intercepted  by  the  air  which  carries  it ; 
and  yet  patchouli  acts  more  feebly  on  radiant  heat  than 
any  other  perfume  yet  examined.  Here  follow  the  results 
obtained  with  various  essential  oils,  the  odor,  in  each  case, 
being  carried  by  a  current  of  dry  air  into  the  tube  already 
employed  for  gases  and  vapors  : 

Name  of  perfume.  Absorption. 

Patchouli 30 

Sandal-wood 32 

Geranium 33 

Oil  of  cloves 34 

Otto  of  roses 37 

Bergamot 44 

Neroli 47 

Lavender 60 

Lemon 65 

Portugal 67 

Thyme 68 

Rosemary 74 

Oil  of  laurel 80 

Camomile-flowers 87 

Cassia 109 

Spikenard 355 

Aniseseed 372 

Thus  the  absorption  by  a  tube  full  of  dry  air  being  1, 
that  of  the  odor  of  patchouli  diffused  in  it  is  30,  that  of 


RADIATION.  195 

lavender  60,  that  of  rosemary  74,  while  that  of  aniseseed 
amounts  to  372.  It  would  be  idle  to  speculate  on  the 
quantities  of  matter  concerned  in  these  actions. 

12.  Aqueous  Vapor  in  relation  to  the  Terrestrial 
Temperatures. * 

We  are  now  fully  prepared  for  a  result  which,  without 
such  preparation,  might  appear  incredible.  Water  is,  to 
some  extent,  a  volatile  body,  and  our  atmosphere,  resting 
as  it  does  upon  the  surface  of  the  ocean,  receives  from  it  a 
continual  supply  of  aqueous  vapor.  It  would  be  an  error 
to  confound  clouds  or  fog  or  any  visible  mist  with  the  va- 
por of  water :  this  vapor  is  a  perfectly  impalpable  gas,  dif- 
fused, even  on  the  clearest  days,  throughout  the  atmosphere. 
Compared  with  the  great  body  of  the  air,  the  aqueous  vapor 
it  contains  is  of  almost  infinitesimal  amount,  99J  out  of 
every  100  parts  of  the  atmosphere  being  composed  of  oxy- 
gen and  nitrogen.  In  the  absence  of  experiment,  we  should 
never  think  of  ascribing  to  this  scant  and  varying  constitu- 
ent any  important  influence  on  terrestrial  radiation ;  and 
yet  its  influence  is  far  more  potent  than  that  of  the  great 
body  of  the  air.  To  say  that  on  a  day  of  average  humidity 
in  England,  the  atmospheric  vapor  exerts  100  times  the 
action  of  the  air  itself,  would  certainly  be  an  understate- 
ment of  the  fact.  The  peculiar  qualities  of  this  vapor,  and 
the  circumstance  that  at  ordinary  temperatures  it  is  very 
near  its  point  of  condensation,  render  the  results  which  it 
yields  in  the  apparatus  already  described,  less  than  the 
truth  ;  and  I  am  not  prepared  to  say  that  the  absorption  by 
this  substance  is  not  200  times  that  of  the  air  in  which  it  is 
diffused.  Comparing  a  single  molecule  of  aqueous  vapor 
with  an  atom  of  either  of  the  main  constituents  of  our  at- 
mosphere, I  am  not  prepared  to  say  how  many  thousand 
times  the  action  of  the  former  exceeds  that  of  the  latter. 
1  See  Note  at  the  end  of  this  Lecture. 


196  FRAGMENTS  OF  SCIENCE. 

But  it  must  be  borne  in  mind  that  these  large  numbers 
depend  in  part  upon  the  extreme  feebleness  of  the  air ;  the 
power  of  aqueous  vapor  seems  vast,  because  that  of  the  air 
with  which  it  is  compared  is  infinitesimal.  Absolutely  con- 
sidered, however,  this  substance,  notwithstanding  its  small 
specific  gravity,  exercises  a  very  potent  action.  Probably 
from  10  to  15  per  cent,  of  the  heat  radiated  from  the  earth 
is  absorbed  within  10  feet  of  the  earth's  surface.  This 
must  evidently  be  of  the  utmost  consequence  to  the  life  of 
the  world.  Imagine  the  superficial  molecules  of  the  earth 
trembling  with  the  motion  of  heat,  and  imparting  it  to  the 
surrounding  ether ;  this  motion  would  be  carried  rapidly 
away,  and  lost  forever  to  our  planet,  if  the  waves  of  ether 
had  nothing  but  the  air  to  contend  with  in  their  outward 
course.  But  the  aqueous  vapor  takes  up  the  motion  of  the 
ethereal  waves,  and  becomes  thereby  heated,  thus  wrapping 
the  earth  like  a  warm  garment,  and  protecting  its  surface 
from  the  deadly  chill  which  it  would  otherwise  sustain. 
Various  philosophers  have  speculated  on  the  influence  of 
an  atmospheric  envelope.  De  Saussure,  Fourier,  M.  Pouil- 
let  and  Mr.  Hopkins  have,  one  and  all,  enriched  scientific 
literature  with  contributions  on  this  subject,  but  the  con- 
siderations which  these  eminent  men  have  applied  to  atmos- 
pheric air,  have,  if  my  experiments  be  correct,  to  be  trans- 
ferred to  the  aqueous  vapor. 

The  observations  of  meteorologists  furnish  important, 
though  hitherto  unconscious  evidence  of  the  influence  of 
this  agent.  Wherever  the  air  is  dry  we  are  liable  to  daily 
extremes  of  temperature.  By  day,  in  such  places,  the  sun's 
heat  reaches  the  earth  unimpeded,  and  renders  the  maxi- 
mum high ;  by  night,  on  the  other  hand,  the  earth's  heat 
escapes  unhindered  into  space,  and  renders  the  minimum 
low.  Hence  the  difference  between  the  maximum  and  min- 
imum is  greatest  where  the  air  is  driest.  In  the  plains 
of  India,  on  the  heights  of  the  Himalaya,  in  central  Asia,  in 


KADIATION.  197 

Australia — wherever  drought  reigns,  we  have  the  heat  of 
day  forcibly  contrasted  with  the  chill  of  night.  In  the  Sa- 
hara itself,  when  the  sun's  rays  cease  to  impinge  on  the 
burning  soil,  the  temperature  runs  rapidly  down  to  freezing, 
because  there  is  no  vapor  overhead  to  check  the  calorific 
drain.  And  here  another  instance  might  be  added  to  the 
numbers  already  known,  in  which  Nature  tends  as  it  were 
to  check  her  own  excess.  By  nocturnal  refrigeration,  the 
aqueous  vapor  of  the  air  is  condensed  to  water  on  the  sur- 
face of  the  earth,  and  as  only  the  superficial  portions  ra- 
diate, the  act  of  condensation  makes  water  the  radiating 
body.  Now  experiment  proves  that  to  the  rays  emitted  by 
water,  aqueous  vapor  is  especially  opaque.  Hence  the  very 
act  of  condensation,  consequent  on  terrestrial  cooling,  be* 
comes  a  safeguard  to  the  earth,  imparting  to  its  radiation 
that  particular  character  which  renders  it  most  liable  to  be 
prevented  from  escaping  into  space. 

It  might  however  be  urged  that,  inasmuch  as  we  derive 
all  our  he^t  from  the  sun,  the  self-same  covering  which  pro- 
tects the  earth  from  chill  must  also  shut  out  the  solar  ra- 
diation. This  is  partially  true,  but  only  partially ;  the 
sun's  rays  are  different  in  quality  from  the  earth's  rays,  and 
it  does  not  at  all  follow  that  the  substance  which  absorbs 
the  one  must  necessarily  absorb  the  other.  Through  a 
layer  of  water,  for  example,  one-tenth  of  an  inch  in  thick- 
ness, the  sun's  rays  are  transmitted  with  comparative  free- 
dom ;  but  through  a  layer  half  this  thickness,  as  Melloni  has 
proved,  no  single  ray  from  the  warmed  earth  could  pass. 
In  like  manner,  the  sun's  rays  pass  with  comparative  free- 
dom through  the  aqueous  vapor  of  the  air ;  the  absorbing 
power  of  this  substance  being  mainly  exerted  upon  the  heat 
that  endeavors  to  escape  from  the  earth.  In  consequence 
of  this  differential  action  upon  solar  and  terrestrial  heat, 
the  mean  temperature  of  our  planet  is  higher  than  is  due  to 
its  distance  from  the  sun. 


198  FRAGMENTS  OF  SCIENCE. 


13.  Liquids  and  their  Vapors  in  relation  to  Radiant 
Heat. 

The  deportment  here  assigned  to  atmospheric  vapor  has 
been  established  by  direct  experiments  on  air  taken  from 
the  streets  and  parks  of  London,  from  the  downs  of  Epsorn, 
from  the  hills  and  sea-beach  of  the  Isle  of  Wight,  and  also 
by  experiments  on  air  in  the  first  instance  dried,  and  after- 
ward rendered  artificially  humid  by  pure  distilled  water. 
It  has  also  been  established  in  the  following  way :  Ten 
volatile  liquids  were  taken  at  random  and  the  power  of 
these  liquids,  at  a  common  thickness,  to  intercept  the  waves 
of  heat  was  carefully  determined.  The  vapors  of  the  liquids 
were  next  taken,  in  quantities  proportional  to  the  quantities 
of  liquid,  and  the  power  of  the  vapors  to  intercept  the  waves 
of  heat  was  also  determined.  Commencing  with  the  sub- 
stance which  exerted  the  least  absorptive  power,  and  pro- 
ceeding upward  to  the  most  energetic,  the  following  order 
of  absorption  was  observed : 

Liquids.  Vapors. 

Bisulphide  of  carbon.  Bisulphide  of  carbon. 

Chloroform.  Chloroform. 

Iodide  of  methyl.  Iodide  of  methyl. 

Iodide  of  ethyl.  Iodide  of  ethyl. 

Benzol.  Benzol. 

Amylene.  Amylene. 

Sulphuric  ether.  Sulphuric  ether. 

Acetic  ether.  Acetic  ether. 

Formic  ether.  Formic  ether. 

Alcohol.  Alcohol. ' 
Water. 

We  here  find  the  order  of  absorption  in  both  cases  to 
be  the  same.  We  have  liberated  the  molecules  from  the 
bonds  which  trammel  them  more  or  less  in  a  liquid  condi- 
tion ;  but  this  change  in  their  state  of  aggregation  does  not 


RADIATION.  199 

change  their  relative  powers  of  absorption.  Nothing  could 
more  clearly  prove  that  the  act  of  absorption  depends  upon 
the  individual  molecule,  which  equally  asserts  its  power  in 
the  liquid  and  the  gaseous  state.  We  may  assuredly  con- 
clude from  the  above  table  that  the  position  of  a  vapor  is 
determined  by  that  of  its  liquid.  Now,  at  the  very  foot  of 
the  list  of  liquids  stands  water,  signalizing  itself  above  all 
others  by  its  enormous  power  of  absorption.  And  from 
this  fact,  even  if  no  direct  experiment  on  the  vapor  of  water 
had  ever  been  made,  we  should  be  entitled  to  rank  that 
vapor  as  the  most  powerful  absorber  of  radiant  heat  hitherto 
discovered.  It  has  been  proved  by  experiment  that  a  shell 
of  air  two  inches  in  thickness  surrounding  our  planet,  and 
saturated  with  the  vapor  of  sulphuric  ether,  would  intercept 
35  per  cent,  of  the  earth's  radiation.  And  though  the 
quantity  of  aqueous  vapor  necessary  to  saturate  air  is 
much  less  than  the  amount  of  sulphuric  ether  vapor  which 
it  can  sustain,  it  is  still  extremely  probable  that  the  esti- 
mate already  made  of  the  action  of  atmospheric  vapor 
within  10  feet  of  the  earth's  surface,  is  altogether  under 
the  mark ;  and  that  we  are  ^indebted  to  this  wonderful  sub- 
stance, to  an  extent  not  accurately  determined,  but  certainly 
far  beyond  what  has  hitherto  been  imagined,  for  the  tem- 
perature now  existing  at  the  surface  of  the  globe. 

14.  Reciproctiy  of  Radiation  and  Absorption. 

Throughout  the  reflections  which  have  hitherto  occupied 
us,  the  image  before  the  mind  has  been  that  of  a  radiant 
source  generating  calorific  waves,  which,  on  passing  among 
the  scattered  molecules  of  a  gas  or  vapor,  were  intercepted 
by  those  molecules  in  various  degrees.  In  all  cases  it  was 
the  transference  of  motion  from  the  ether  to  the  compara- 
tively quiescent  molecules  of  the  gas  or  vapor.  We  have 
now  to  change  the  form  of  our  conception,  and  to  figure 


200  FRAGMENTS  OF  SCIENCE. 

these  molecules  not  as  absorbers,  but  as  radiators, 'not  as 
the  recipients,  but  as  the  originators  of  wave  motion.  That 
is  to  say,  we  must  figure  them  vibrating  and  generating  in 
the  surrounding  ether  undulations  which  speed  through  it 
with  the  velocity  of  light.  Our  object  now  is  to  inquire 
whether  the  act  of  chemical  combination,  which  proves  so 
potent  as  regards  the  phenomena  of  absorption,  does  not 
also  manifest  its  power  in  the  phenomena  of  radiation.  For 
the  examination  of  this  question  it  is  necessary,  in  the  first 
place,  to  heat  our  gases  and  vapors  to  the  same  tempera- 
ture, and  then  examine  their  power  of  discharging  the 
motion  thus  imparted  to  them  upon  the  ether  in  which 
they  swing. 

A  heated  copper  ball  was  placed  above  a  ring  gas- 
burner  possessing  a  great  number  of  small  apertures,  the 
burner  being  connected  by  a  tube  with  vessels  containing 
the  various  gases  to  be  examined.  By  gentle  pressure  the 
gases  were  forced  through  the  orifices  of  the  burner  against 
the  copper  ball,  where  each  of  them,  being  heated,  rose  in 
an  ascending  column.  A  thermo-electric  pile,  entirely 
screened  off  from  the  hot  ball,  was  exposed  to  the  radiation 
of  the  warm  gas,  and  the  deflection  of  a  magnetic  needle 
connected  with  the  pile  declared  the  energy  of  the  radia- 
tion. 

By  this  mode  of  experiment  it  was  proved  that  the  self- 
same molecular  arrangement  which  renders  a  gas  a  power- 
ful absorber,  renders  it  in  the  same  degree  a  powerful 
radiator — that  the  atom  or  molecule  which  is  competent  to 
intercept  the  calorific  waves  is  in  the  same  degree  compe- 
tent to  generate  them.  Thus,  while  the  atoms  of  element- 
ary gases  proved  themselves  unable  to  emit  any  sensible 
amount  of  radiant  heat,  the  molecules  of  compound  gases 
were  shown  to  be  capable  of  powerfully  disturbing  the  sur- 
rounding ether.  By  special  modes  of  experiment  the  same 
was  proved  to  hold  good  for  the  vapors  of  volatile  liquids, 


RADIATION.  201 

the  radiative  power  of  every  vapor  being  found  proportional 
to  its  absorptive  power. 

The  method  of  experiment  here  pursued,  though  not  of 
the  simplest  character,  is  still  within  your  grasp.  When 
air  is  permitted  to  rush  into  an  exhausted  tube,  the  tem- 
perature of  the  air  is  raised  to  a  degree  equivalent  to  the 
vis  viva  extinguished.1  Such  air  is  said  to  be  dynamically 
heated,  and  if  pure,  it  shows  itself  incompetent  to  radiate, 
even  when  a  rock-salt  window  is  provided  for  the  passage 
of  its  rays.  But  if  instead  of  being  empty  the  tube  contain 
a  small  quantity  of  vapor,  then  the  warmed  air  will  com- 
municate heat  by  contact  to  the  vapor,  which  will  be  thus 
enabled  to  radiate.  Thus  the  molecules  of  the  vapor  con- 
vert into  the  radiant  form  the  heat  imparted  dynamically 
to  the  atoms  of  the  air.  By  this  process,  which  has  been 
called  dynamic  radiation,  the  radiative  power  of  both  vapors 
and  gases  has  been  determined,  and  the  reciprocity  of  their 
radiation  and  absorption  proved.2 

In  the  excellent  researches  of  Leslie,  De  la  Provostaye 
and  Desains,  and  Balfour  Stewart,  the  reciprocity  of  radia- 
tion and  absorption  as  regards  solid  bodies  has  been  vari- 
ously illustrated ;  while  the  labors,  theoretical  and  experi- 
mental, of  Kirchhoff  have  given  this  subject  a  wonderful 
expansion,  and  enriched  it  by  applications  of  the  highest 
kind.  To  their  results  are  now  to  be  added  the  foregoing, 
whereby  gases  and  vapors  which  have  been  hitherto  thought 
inaccessible  to  experiments  of  this  kind  are  proved  to  ex- 
hibit the  duality  of  radiation  and  absorption,  the  influence 
on  both  of  chemical  combination  being  exhibited  in  the 
most  decisive  and  extraordinary  way. 

1  See  page  20  for  a  definition  of  vis  viva. 

2  When  heated,  air  imparts  its  motion  to  another  gas  or  vapor;  the 
transference  of  heat  is  accompanied  by  a  change  of  vibrating  period.    The 
dynamic  radiation  of  vapors  is  rendered  possible  by  the  transmutation  of 
vibrations. 


202  FRAGMENTS  OF  SCIENCE. 


15.  Influence  of  Vibrating  Period  and  Molecular  Form. 
Physical  Analysis  of  the  Human  Breath. 

In  the  foregoing  experiments  with  gases  and  vapors  we 
have  employed  throughout  invisible  rays ;  some  of  these 
bodies  are  so  impervious  that  in  lengths  of  a  few  feet  only 
they  intercept  every  ray  as  effectually  as  a  layer  of  pitch 
would  do.  The  substances,  however,  which  show  themselves 
thus  opaque  to  radiant  heat  are  perfectly  transparent  to 
light.  Now  the  T&ys  of  light  differ  from  those  of  invisible 
heat  only  in  point  of  period,  the  former  failing  to  affect  the 
retina  because  their  periods  of  recurrence  are  too  slow. 
Hence,  in  some  way  or  other  the  transparency  of  our  gases 
and  vapors  depends  upon  the  periods  of  the  waves  which 
impinge  upon  them.  What  is  the  nature  of  this  depend- 
ence ?  The  admirable  researches  of  Kirchhoff  help  us  to  an 
answer.  The  atoms  and  molecules  of  every  gas  have  cer- 
tain definite  rates  of  oscillation,  and  those  waves  of  ether 
are  most  copiously  absorbed  whose  periods  of  recurrence 
synchronize  with  the  periods  of  the  molecules  among  which 
they  pass.  Thus,  when  we  find  the  invisible  rays  absorbed 
and  the  visible  ones  transmitted  by  a  layer  of  gas,  we  con- 
clude that  the  oscillating  periods  of  the  gaseous  molecules 
coincide  with  those  of  the  invisible,  and  not  with  those  of 
the  visible  spectrum. 

It  requires  some  discipline  of  the  imagination  to  form  a 
clear  picture  of  this  process.  Such  a  picture  is,  however, 
possible,  and  ought  to  be  obtained.  When  the  waves  of 
ether  impinge  upon  molecules  whose  periods  of  vibration 
coincide  with  the  recurrence  of  the  undulations,  the  timed 
strokes  of  the  waves,  the  vibration  of  the  molecules  aug- 
ments, as  a  heavy  pendulum  is  set  in  motion  by  well-timed 
puffs  of  breath.  Millions  of  millions  of  shocks  are  received 
every  second  from  the  calorific  waves,  and  it  is  not  difficult 


RADIATION.  203 

to  see  that,  as  every  wave  arrives  just  in  time  to  repeat  the 
action  of  its  predecessor,  the  molecules  must  finally  be 
caused  to  swing  through  wider  spaces  than  if  the  arrivals 
were  not  so  timed.  In  fact,  it  is  not  difficult  to  see  that  an 
assemblage  of  molecules,  operated  upon  by  contending 
waves,  might  remain  practically  quiescent,  and  this  is  act- 
ually the  case  when  the  waves  of  the  visible  spectrum  pass 
through  a  transparent  gas  or  vapor.  There  is  here  no  sen- 
sible transference  of  motion  from  the  ether  to  the  molecules ; 
in  other  words,  there  is  no  sensible  absorption  of  heat. 

One  striking  example  of  the  influence  of  period  may  here 
be  recorded.  Carbonic-acid  gas  is  one  of  the  feeblest  of 
absorbers  of  the  radiant  heat  emitted  by  solid  sources.  It 
is,  for  example,  to  a  great  extent  transparent  to  the  rays 
emitted  by  the  heated  copper-plate  already  referred  to. 
There  are,  however,  certain  rays,  comparatively  few  in  num- 
ber, emitted  by  the  copper,  to  which  the  carbonic  acid  is 
impervious  ;  and  could,  we  obtain  a  source  of  heat  emitting 
such  rays  only,  we  should  find  carbonic  acid  more  opaque  to 
the  radiation  from  that  source  than  any  other  gas.  Such  a 
source  is  actually  found  in  the  flame  of  carbonic  oxide, 
where  hot  carbonic  acid  constitutes  the  main  radiating  body. 
Of  the  rays  emitted  by  our  heated  plate  of  copper,  olefiant 
gas  absorbs  ten  times  the  quantity  absorbed  by  carbonic 
acid.  Of  the  rays  emitted  by  a  carbonic-oxide  flame,  car- 
bonic acid  absorbs  twice  as  much  as  olefiant  gas.  This  won- 
derful change  in  the  power  of  the  former  as  an  absorber  is 
simply  due  to  the  fact  that  the  periods  of  the  hot  and  cold 
carbonic  acid  are  identical,  and  that  the  waves  from  the 
flame  freely  transfer  their  motion  to  the  molecules  which 
synchronize  with  them.  Thus  it  is  that  the  tenth  of  an  at- 
mosphere of  carbonic  acid,  enclosed  in  a  tube  four  feet  long, 
absorbs  60  per  cent,  of  the  radiation  from  a  carbonic-oxide 
flame,  while  one-thirtieth  of  an  atmosphere  absorbs  48  per 
cent,  of  the  heat  from  the  same  origin. 


204  FRAGMENTS  OF  SCIENCE. 

In  fact,  the  presence  of  the  minutest  quantity  of  car- 
bonic acid  may  be  detected  by  its  action  on  the  rays  from 
the  carbonic-oxide  flame.  Carrying,  for  example,  the  dried 
human  breath  into  a  tube  four  feet  long,  the  absorption 
there  effected  by  the  carbonic  acid  of  the  breath  amounts 
to  50  per  cent,  of  the  entire  radiation.  Radiant  heat  may 
indeed  be  employed  as  a  means  of  determining  practically 
the  amount  of  carbonic  acid  expired  from  the  lungs.  My 
late  assistant,  Mr.  Barrett,  has  made  this  determination. 
The  absorption  produced  by  the  breath  freed  from  its  moist- 
ure, but  retaining  its  carbonic  acid,  was  first  determined. 
Carbonic  acid  artificially  prepared  was  then  mixed  with  dry 
air  in  such  proportions  that  the  action  of  the  mixture  upon 
the  rays  of  heat  was  the  same  as  that  of  the  dried  breath. 
The  percentage  of  the  former  being  known,  immediately 
gave  that  of  the  latter.  The  same  breath  analyzed  chemi- 
cally by  Dr.  Frankland,  and  physically  by  Mr.  Barrett,  gave 
the  following  results : 

Percentage  of  Carbonic  Acid  in  the  Human  Breath. 

Chemical  analysis.  Physical  analysis. 

4.66 4.56 

6.33 5.22 

It  is  thus  proved  that  in  the  quantity  of  ethereal  motion 
which  it  is  competent  to  take  up,  we  have  a  practical  meas- 
ure of  the  carbonic  acid  of  the  breath,  and  hence  of  the 
combustion  going  on  in  the  human  lungs. 

Still  this  question  of  period,  though  of  the  utmost  im- 
portance, is  not  competent  to  account  for  the  whole  of  the 
observed  facts.  The  ether,  as  far  as  we  know,  accepts 
vibrations  of  all  periods  with  the  same  readiness.  To  it 
the  oscillations  of  an  atom  of  oxygen  are  just  as  acceptable 
as  those  of  a  molecule  of  olefiant  gas ;  that  the  vibrating 
oxygen  then  stands  so  far  below  the  olefiant  gas  in  radiant 


RADIATION.  205 

power  must  be  referred  not  to  period,  but  to  some  other 
peculiarity  of  the  elementary  gas.  The  atomic  group  which 
constitutes  the  molecule  of  olefiant  gas,  produces  many 
thousand  times  the  disturbance  caused  by  the  oxygen,  be- 
cause the  group  is  able  to  lay  a  vastly  more  powerful  hold 
upon  the  ether  than  the  single  atoms  can,  The  cavities  and 
indentations  of  a  molecule  composed  of  spherical  atoms 
may  be  one  cause  of  this  augmented  hold.  Another,  and 
probably  very  potent  one  may  be,  that  the  ether  itself,  con- 
densed and  entangled  among  the  constituent  atoms  of  a 
compound,  virtually  increases  the  magnitude  of  the  group, 
and  hence  augments  the  disturbance.  But  whatever  may 
be  the  fate  of  these  attempts  to  visualize  the  physics  of  the 
process,  it  will  still  remain  true  that,  to  account  for  the 
phenomena  of  radiation  and  absorption  we  must  take  into 
consideration  the  shape,  size,  and  complexity  of  the  mole- 
cules by  which  the  ether  is  disturbed. 

16.  Summary  and  Conclusion. 

Let  us  now  cast  a  momentary  glance  over  the  ground 
that  we  have  left  behind.  The  general  nature  of  light  and 
heat  was  first  briefly  described  :  the  compounding  of  matter 
from  elementary  atoms  and  the  influence  of  the  act  of  com- 
bination on  radiation  and  absorption  were  considered  and 
experimentally  illustrated.  Through  the  transparent  ele- 
mentary gases  radiant  heat  was  found  to  pass  as  through  a 
vacuum,  while  many  of  the  compound  gases  presented 
almost  impassable  obstacles  to  the  calorific  waves.  This 
deportment  of  the  simple  gases  directed  our  attention  to 
other  elementary  bodies,  the  examination  of  which  led  to 
the  discovery  that  the  element  iodine,  dissolved  in  bisul- 
phide of  carbon,  possesses  the  power  of  detaching,  with 
extraordinary  sharpness,  the  light  of  the  spectrum  from  its 
heat,  intercepting  all  luminous  rays  up  to  the  extreme  red, 


206  FRAGMENTS  OF  SCIENCE. 

and  permitting  the  calorific  rays  beyond  the  red  to  pass 
freely  through  it.  This  substance  was  then  employed  to 
filter  the  beams  of  the  electric  light,  and  to  form  foci  of . 
invisible  rays  so  intense  as  to  produce  almost  all  the  effects 
obtainable  in  an  ordinary  fire.  Combustible  bodies  were 
burnt  and  refractory  ones  were  raised  to  a  white  heat  by  the 
concentrated  invisible  rays.  Thus,  by  exalting  their  re- 
frangibility,  the  invisible  rays  of  the  electric  light  were 
rendered  visible,  and  all  the  colors  of  the  solar  spectrum 
were  extracted  from  utter  darkness.  The  extreme  richness 
of  the  electric  light  in  invisible  rays  of  low  refrangibility 
was  demonstrated,  one-ninth  only  of  its  radiation  consisting 
of  luminous  rays.  The  deadness  of  the  optic  nerve  to  those 
invisible  rays  was  proved,  and  experiments  were  then 
added,  to  show  that  the  bright  and  the  dark  rays  of  a 
solid  body  raised  gradually  to  intense  incandescence,  are 
strengthened  together  ;  intense  dark  heat  being  an  inva- 
riable accompaniment  of  intense  white  heat.  A  sun  could 
not  be  formed,  or  a  meteorite  rendered  luminous,  on  any 
other  condition.  The  light-giving  rays,  constituting  only  a 
small  fraction  of  the  total  radiation,  their  unspeakable  im- 
portance to  us  is  due  to  the  fact  that  their  periods  are 
attuned  to  the  special  requirements  of  the  eye. 

Among  the  vapors  of  volatile  liquids  vast  differences 
were  also  found  to  exist,  as  regards  their  powers  of  absorp- 
tion. We  followed  various  molecules  from  a  state  of  liquid 
to  a  state  of  gas,  and  found  in  both  states  of  aggregation, 
the  power  of  the  individual  molecules  equally  asserted. 
The  position  of  a  vapor  as  an  absorber  of  radiant  heat  was 
shown  to  be  determined  by  that  of  the  liquid  from  which  it 
is  derived.  Reversing  our  conceptions,  and  regarding  the 
molecules  of  gases  and  vapors  not  as  the  recipients,  but  as 
the  originators  of  wave-motion;  not  as  absorbers  but  as 
radiators ;  it  was  proved  that  the  powers  of  absorption  and 
radiation  went  hand  in  hand,  the  self-same  chemical  act 


RADIATION.  207 

which  rendered  a  body  competent  to  intercept  the  waves 
of  ether,  rendering  it  competent  in  the  same  degree  to  gen- 
erate them.  Perfumes  were  next  subjected  to  examination, 
and  notwithstanding  their  extraordinary  tenuity,  they  were 
found  vastly  superior,  in  point  of  absorptive  power,  to  the 
body  of  the  air  in  which  they  were  diffused.  We  were  led 
thus  slowly  up  to  the  examination  of  the  most  widely 
diffused  and  most  important  of  all  vapors — the  aqueous 
vapor  of  our  atmosphere — and  we  found  in  it  a  potent 
absorber  of  the  purely  calorific  rays.  The  power  of  this 
substance  to  influence  climate,  and  its  general  influence 
on  the  temperature  of  the  earth,  were  then  briefly  dwelt 
upon.  A  cobweb  spread  above  a  blossom  is  sufficient  to 
protect  it  jrom  nightly  chill ;  and  thus  the  aqueous  vapor 
of  our  air,  attenuated  as  it  is,  checks  the  drain  of  terrestrial 
heat,  and  saves  the  surface  of  our  planet  from  the  refriger- 
ation which  would  assuredly  accrue,  were  no  such  sub- 
stance interposed  between  it  and  the  voids  of  space.  We 
considered  the  influence  of  vibrating  period  and  molecular 
form  on  absorption  and  radiation,  and  finally  deduced,  from 
its  action  upon  radiant  heat,  the  exact  amount  of  carbonic 
acid  expired  by  the  human  lungs. 

Thus  in  brief  outline  were  placed  before  you  some  of 
the  results  of  recent  inquiries  in  the  domain  of  Radiation, 
and  my  aim  throughout  has  been  to  raise  in  your  minds 
distinct  physical  images  of  the  various  processes  involved 
in  our  researches.  It  is  thought  by  some  that  natural 
science  has  a  deadening  influence  on  the  imagination,  and 
a  doubt  might  fairly  be  raised  as  to  the  value  of  any  study 
which  would  necessarily  have  this  effect.  But  the  experi- 
ence of  the  last  hour  must,  I  think,  have  convinced  you 
that  the  study  of  natural  science  goes  hand  in  hand  with 
the  culture  of  the  imagination.  Throughout  the  greater 
part  of  this  discourse  we  have  been  sustained  by  this 
faculty.  We  have  been  picturing  atoms,  and  molecules, 


208  FRAGMENTS  OF  SCIENCE. 

and  vibrations,  and  waves,  which  eye  has  never  seen  nor 
ear  heard,  and  which  can  only  be  discerned  by  the  exercise 
of  imagination.  This,  in  fact,  is  the  faculty  which  enables 
us  to  transcend  the  boundaries  of  sense,  and  connect  the 
phenomena  of  our  visible  world  with  those  of  an  invisible 
one.  Without  imagination  we  never  could  have  risen  to 
the  conceptions  which  have  occupied  us  here  to-day ;  and 
in  proportion  to  your  power  of  exercising  this  faculty  aright, 
and  of  associating  definite  mental  images  with  the  terms 
employed,  will  be  the  pleasure  and  the  profit  which  you 
will  derive  from  this  lecture.  The  outward  facts  of  Nature 
are  insufficient  to  satisfy  the  mind.  We  cannot  be  content 
with  knowing  that  the  light  and  heat  of  the  sun  illuminate 
and  warm  the  world.  We  are  led  irresistibly  to  inquire 
what  is  light,  and  what  is  heat  ?  and  this  question  leads  us 
at  once  out  of  the  region  of  sense  into  that  of  imagination. 
Thus  pondering,  and  questioning,  and  striving  to  sup- 
plement that  which  is  felt  and  seen,  but  which  is  incom- 
plete, by  something  unfelt  and  unseen  which  is  necessary 
to  its  completeness,  men  of  genius  have  in  part  discerned, 
not  only  the  nature  of  light  and  heat,  but  also,  through 
them,  the  general  relationship  of  natural  phenomena.  The 
working  power  of  Nature  is  the  power  of  actual  or  poten- 
tial motion,  of  which  all  its  phenomena  are  but  special 
forms.  This  motion  manifests  itself  in  tangible  and  in  in- 
tangible matter,  being  incessantly  transferred  from  the  one 
to  the  other,  and  incessantly  transformed  by  the  change. 
It  is  as  real  in  the  waves  of  the  ether  as  in  the  waves  of 
the  sea ;  the  latter,  derived  as  they  are  from  winds,  which 
in  their  turn  are  derived  from  the  sun,  being  nothing  more 
than  the  heaped-up  motion  of  the  former.  It  is  the  calo- 
rific waves  emitted  by  the  sun  which  heat  our  air,  produce 
our  winds,  and  hence  agitate  our  ocean.  And  whether  they 
break  in  foam  upon  the  shore,  or  rub  silently  against  the 
ocean's  bed,  or  subside  by  the  mutual  friction  of  their  own 


RADIATION.  209 

parts,  the  sea-waves,  which  cannot  subside  without  pro- 
ducing heat,  finally  resolve  themselves  into  waves  of  ether, 
thus  regenerating  the  motion  from  which  their  temporary 
existence  was  derived.  This  connection  is  typical.  Nature 
is  not  an  aggregate  of  independent  parts,  but  an  organic 
whole.  If  you  open  a  piano  and  sing  into  it,  a  certain 
string  will  respond.  Change  the  pitch  of  your  voice  ;  the 
first  string  ceases  to  vibrate,  but  another  replies.  Change 
again  the  pitch ;  the  first  two  strings  are  silent,  while  an- 
other resounds.  Now,  in  altering  the  pitch  you  simply 
change  the  form  of  the  motion  communicated  by  your  vocal 
chords  to  the  air,  one  string  responding  to  one  form,  and 
another  to  another.  And  thus  is  sentient  man  acted  on  by 
Nature,  the  optic,  the  auditory,  and  other  nerves  of  the 
human  body  being  so  many  strings  differently  tuned  and 
responsive  to  different  forms  of  the  universal  power. 


NOTE. — The  statements  regarding  the  action  of  aqueous  vapor,  made 
in  sections  12  and  13  of  this  Lecture,  have  been  controverted  by  the  late 
Professor  Magnus,  of  Berlin.  I  therefore  wish  the  reader  to  hold  in  sus- 
pension his  judgment  of  these  two  sections  until  new  light  can  be  thrown 
upon  the  subject.  This  will  soon  be  done. 


IX. 
ON  RADIANT  HEAT 


IN  RELATION  TO  THE  COLOR  AND  CHEMICAL  CONSTITUTION 
OF  BODIES. 

A  DISCOURSE. 

DELIVEKED  IN  THE  EOYAL  INSTITUTION  OF  GKEAT  BKITAIN. 

January  19,  1866. 


"  I  took  a  number  of  little  square  pieces  of  broadcloth  from  a  tailor's 
pattern-card,  of  various  colors.  They  were  black,  deep  blue,  lighter  blue, 
green,  purple,  red,  yellow,  white,  and  other  colors,  or  shades  of  color.  I 
laid  them  all  out  upon  the  snow  on  a  bright,  sunshiny  morning.  In  a  few 
hours  (I  cannot  now  be  exact  as  to  the  time),  the  black,  being  warmed 
most  by  the  sun,  was  sunk  so  low  as  to  be  below  the  stroke  of  the  sun's 
rays  ;  the  dark  blue  almost  as  low,  the  lighter  blue  not  quite  so  much  as 
the  dark,  the  other  colors  less  as  they  were  lighter.  The  white  remained 
on  the  surface  of  the  snow,  not  having  entered  it  at  all. 

"  What  signifies  philosophy  that  does  not  apply  to  some  use  ?  May 
we  not  learn  from  hence  that  black  clothes  are  not  so  fit  to  wear  in  a  hot, 
sunny  climate  or  season  as  white  ones  ;  because  in  such  clothes  the  body 
is  more  heated  by  the  sun  when  we  walk  abroad,  and  are  at  the  same  time 
heated  by  the  exercise,  which  double  heat  is  apt  to  bring  on  putrid,  dan- 
gerous fevers  ?  That  soldiers  and  seamen,  who  must  march  and  labor  in 
the  sun,  should,  in  the  East  or  West  Indies,  have  a  uniform  of  white  ? 
That  summer  hats  for  men  or  women  should  be  white,  as  repelling  that 
heat  which  gives  headaches  to  so  many,  and  to  some  the  fatal  stroke  that 
the  French  call  coup  de  soleil  ?  That  the  ladies'  summer  hats,  however, 
should  be  lined  with  black,  as  not  reverberating  on  their  faces  those  rays 
which  are  reflected  upward  from  the  earth  or  water  ?  That  the  putting 
of  a  white  cap  of  paper  or  linen  within  the  crown  of  a  black  hat,  as  most 
do,  will  not  keep  out  the  heat,  though  it  would  if  placed  without  ?  That 
fruit  walls  being  blacked  may  receive  so  much  heat  from  the  sun  in  the 
daytime  as  to  continue  warm  in  some  degree  through  the  night,  and 
thereby  preserve  the  fruit  from  frosts,  or  forward  its  growth — with  sun- 
dry other  particulars  of  greater  or  less  importance  that  will  occur  from 
time  to  time  to  attentive  minds  ?  " 

BENJAMIN  FRANKLIN, 
Letter  to  Miss  Mary  Stevenson. 


IX. 


ON  RADIANT  HEAT  IN  RELATION  TO  THE  COLOR 
AND  CHEMICAL  CONSTITUTION  OF  BODIES. 

ONE  of  the  most  important  functions  of  physical  sci- 
ence, considered  as  a  discipline  of  the  mind,  is  to  enable  us  by 
means  of  the  tangible  processes  of  Nature  to  apprehend  the 
intangible.  The  tangible  processes  give  direction  to  the 
line  of  thought ;  but  this  once  given,  the  length  of  the  line 
is  not  limited  by  the  boundaries  of  the  senses.  Indeed,  the 
domain  of  the  senses  in  Nature  is  almost  infinitely  small  in 
comparison  with  the  vast  region  accessible  to  thought 
which  lies  beyond  them.  From  a  few  observations  of  a 
comet,  when  it  comes  within  the  range  of  his  telescope,  an 
astronomer  can  calculate  its  path  in  regions  which  no  tele- 
scope can  reach ;  and  in  like  manner,  by  means  of  data 
furnished  in  the  narrow  world  of  the  senses,  we  make  our- 
selves at  home  in  other  and  wider  worlds,  which  can  be 
traversed  by  the  intellect  alone. 

From  the  earliest  ages  the  questions, "  What  is  light  ?  " 
and  "  What  is  heat  ?  "  have  occurred  to  the  minds  of  men ; 
but  these  questions  never  would  have  been  answered  had 
they  not  been  preceded  by  the  question,  "  What  is  sound  ?  " 
Amid  the  grosser  phenomena  of  acoustics  the  mind  was 
first  disciplined,  conceptions  being  thus  obtained  from 
direct  observation,  which  were  afterward  applied  to  phe- 
nomena of  a  character  far  too  subtle  to  be  observed  directly. 
Sound  we  know  to  be  due  to  vibratory  motion.  A  vibrating 


214  FRAGMENTS  OF  SCIENCE. 

tuning-fork,  for  example,  moulds  the  air  round  it  into  un- 
dulations or  waves,  which  speed  away  on  all  sides  with  a 
certain  measured  velocity,  impinge  upon  the  drum  of  the 
ear,  shake  the  auditory  nerve,  and  awake  in  the  brain  the 
sensation  of  sound.  When  sufficiently  near  a  sounding 
body,  we  can  feel  the  vibrations  of  the  air.  A  deaf  man, 
for  example,  plunging  his  hand  into  a  bell  when  it  is 
sounded,  feels  through  the  common  nerves  of  his  body  those 
tremors  which,  when  imparted  to  the  nerves  of  healthy  ears, 
are  translated  into  sound.  There  are  various  ways  of  ren- 
dering those  sonorous  vibrations  not  only  tangible  but 
visible;  and  it  was  not  until  numberless  experiments  of 
this  kind  had  been  executed,  that  the  scientific  investigator 
abandoned  himself  wholly,  and  without  a  shadow  of  uncer- 
tainty, to  the  conviction  that  what  is  sound  within  us  is, 
outside  of  us,  a  motion  of  the  air. 

But  once  having  established  this  fact — once  having 
proved  beyond  all  doubt  that  the  sensation  of  sound  is 
produced  by  an  agitation  of  the  nerve  of  the  ear,  the 
thought  soon  suggested  itself  that  light  might  be  due  to 
an  agitation  of  the  nerve  of  the  eye.  This  was  a  great  step 
in  advance  of  that  ancient  notion  which  regarded  light  as 
something  emitted  by  the  eye,  and  not  as  any  thing 
imparted  to  it.  But  if  light  be  produced  by"  an  agitation 
of  the  optic  nerve  or  retina,  what  is  it  that  produces  the 
agitation  ?  Newton,  you  know,  supposed  minute  particles 
to  be  shot  through  the  humors  of  the  eye  against  the 
retina,  which  hangs  like  a  target  at  the  back  of  the  eye. 
The  impact  of  these  particles  against  the  target,  Newton 
believed  to  be  the  cause  of  light.  But  Newton's  notion 
has  not  held  its  ground,  being  entirely  driven  from  the 
field  by  the  more  wonderful  and  far  more  philosophical 
notion  that  light,  like  sound,  is  a  product  of  wave-motion. 

The  domain  in  which  this  motion  of  light  is  carried  on 
lies  entirely  beyond  the  reach  of  our  senses.  The  waves 


RADIANT   HEAT  AND   ITS   RELATIONS.  215 

of  light  require  a  medium  for  their  formation  and  propaga- 
tion, but  we  cannot  see,  or  feel,  or  taste,  or  smell  this 
medium.  How,  then,  has  its  existence  been  established  ? 
By  showing  that  by  the  assumption  of  this  wonderful 
intangible  ether  all  the  phenomena  of  optics  are  accounted 
for  with  a  fulness  and  clearness  and  conclusiveness  which 
leave  no  desire  of  the  intellect  unfulfilled.  When  the  law 
of  gravitation  first  suggested  itself  to  the  mind  of  Newton, 
what  did  he  do  ?  He  set  himself  to  examine  whether  it 
accounted  for  all  the  facts.  He  determined  the  courses  of 
the  planets ;  he  calculated  the  rapidity  of  the  moon's  fall 
toward  the  earth;  he  considered  the  precession  of  the 
equinoxes,  the  ebb  and  flow  of  the  tides,  and  found  all 
explained  by  the  law  of  gravitation.  He  therefore  regarded 
this  law  as  established,  and  the  verdict  of  science  sub- 
sequently confirmed  his  conclusion.  On  similar,  and,  if 
possible,  on  stronger  grounds,  we  found  our  belief  in  the 
existence  of  the  universal  ether.  It  explains  facts  far 
more  various  and  complicated  than  those  on  which  New- 
ton based  his  law.  If  a  single  phenomenon  could  be 
pointed  out  which  the  ether  is  proved  incompetent  to 
explain,  we  should  have  to  give  it  up ;  but  no  such  phe- 
nomenon has  ever  been  pointed  out.  It  is,  therefore,  at 
least  as  certain  that  space  is  filled  with  a  medium  by 
means  of  which  suns  and  stars  diffuse  their  radiant  power, 
as  that  it  is  traversed  by  that  force  which  holds,  not  only 
our  planetary  system,  but  the  immeasurable  heavens  them- 
selves, in  its  grasp. 

There  is  no  more  wonderful  instance  than  this  of  the 
production  of  a  line  of  thought  from  the  world  of  the  senses 
into  the  region  of  pure  imagination.  I  mean  by  imagination 
here,  not  that  play  of  fancy  which  can  give  to  "  airy  nothing 
a  local  habitation  and  a  name,"  but  that  power  which 
enables  the  mind  to  conceive  realities  which  lie  beyond  the 
range  of  the  senses — to  present  to  itself  distinct  physical 


216  FRAGMENTS  OF  SCIENCE. 

images  of  processes  which,  though  mighty  in  the  aggregate 
beyond  all  conception,  are  so  minute  individually  as  to 
elude  all  observation.  It  is  the  waves  of  air  excited  by 
this  tuning-fork  which  render  its  vibrations  audible.  It  is 
the  waves  of  ether  sent  forth  from  those  lamps  overhead 
which  render  them  luminous  to  us  £fout  so  minute  are  these 
waves,  that  it  would  take  from  30,000  to  60,000  of  them 
placed  end  to  end  to  cover  a  single  inch.  Their  number, 
however,  compensates  for  their  minuteness.  Trillions  of 
them  have  entered  your  eyes  and  hit  the  retina  at  the  back 
of  the  eye  in  the  time  consumed  in  the  utterance  of  the 
shortest  sentence  of  this  discourse.  This  is  the  steadfast 
result  of  modern  research  ;  but  we  never  could  have  reached 
it  without  previous  discipline.  ("We  never  could  have 
measured  the  waves  of  light,  nor  even  imagined  them  to 
exist,  had  we  not  previously  exercised  ourselves  among  the 
waves  of  sound.  Sound  and  light  are  now  mutually  help- 
ful, the  conceptions  of  each  being  expanded,  strengthened, 
and  denned,  by  the  conceptions  of  the  other. 

The  ether  which  conveys  the  pulses  of  light  and  heat 
not  only  fills  the  celestial  spaces,  bathing  the  sides  of  suns 
and  planets,  but  it  also  encircles  the  atoms  of  which  these 
suns  and  planets  are  composed.  It  is  the  motion  of  these 
atoms,  and  not  that  of  any  sensible  parts  of  bodies,  that 
the  ether  conveys ;  it  is  this  motion  that  constitutes  the 
objective  cause  of  what  in  our  sensations  are  light  and 
/neat.  An  atom,  then,  sending  its  pulses  through  the  infi- 
\y  nite  ether,  resembles  a  tuning-fork  sending  its  pulses 
through  the  air.  Let  us  look  for  a  moment  at  this  thrilling 
ether,  and  briefly  consider  its  relation  to  the  bodies  whose 
vibrations  it  conveys.  Different  bodies,  when  heated  to  the 
same  temperature,  possess  very  different  powers  of  agitat- 
ing the  ether:  some  are  good  radiators,  others  are  bad 
radiators ;  which  means  that  some  are  so  constituted  as  to 
communicate  their  motion  freely  to  the  ether,  producing 


RADIANT  HEAT  AND  ITS  RELATIONS.  217 

therein  powerful  undulations;  while  others  are  unable 
thus  to  communicate  their  motion,  but  glide  through  the 
ether  without  materially  disturbing  its  repose.  Recent 
experiments  have  proved  that  elementary  bodies,  except 
under  certain  anomalous  conditions,  belong  to  the  class  of 
bad  radiators.  An  atom  vibrating  in  the  ether  resembles 
this  naked  tuning-fork  vibrating  in  the  air.  The  amount 
of  motion  communicated  to  the  air  by  these  thin  prongs  is 
too  small  to  evoke  at  any  distance  the  sensation  of  sound. 
But  if  we  permit  the  atoms  to  combine  chemically  and 
form  molecules,  the  result  in  many  cases  is  an  enormous 
change  in  the  power  of  radiation.  The  amount  of  ethereal 
disturbance  produced  by  the  combined  atoms  of  a  body 
may  be  many  thousand  times  that  produced  by  its  constitu- 
ent atoms  when  uncombined.  The  effect  is  roughly  typi- 
fied by  this  tuning-fork  when  connected  with  its  resonant 
case.  The  fork  and  its  case  now  swing  as  a  compound 
system,  and  the  vibrations  which  were  before  inaudible,  are 
now  the  source  of  a  musical  sound  so  powerful  that  it 
might  be  plainly  heard  by  thousands  at  once.  The  fork 
and  its  case  combined  may  be  roughly  regarded  as  a  good 
radiator  of  sound. 

The  pitch  of  a  musical  note  depends  upon  the  rapidity 
of  its  vibrations,  or,  in  other  words,  on  the  length  of  its 
waves.  Now,  the  pitch  of  a  note  answers  to  the  color  of 
light.  Taking  a  slice  of  white  light  from  the  beam  of  an 
electric  lamp,  I  cause  that  light  to  pass  through  an  arrange- 
ment of  prisms.  It  is  decomposed,  and  we  have  the  effect 
obtained  by  Newton,  who  first  unrolled  the  solar  beam  into 
the  splendors  of  the  solar  spectrum.  At  one  end  of  this 
spectrum  we  have  red  light,  at  the  other  violet,  and  be- 
tween those  extremes  lie  the  other  prismatic  colors.  As 
we  advance  along  the  spectrum  from  the  red  to  the  violet, 
the  pitch  of  the  light — if  I  may  use  the  expression — height- 
ens, the  sensation  of  violet  being  produced  by  a  more  rapid 
10 


218  FRAGMENTS  OF  SCIENCE. 

succession  of  impulses  than  that  which  produces  the  im- 
pression of  red.  The  vibrations  of  the  violet  are  about 
twice  as  rapid  as  those  of  the  red ;  in  other  words,  the 
range  of  the  visible  spectrum  is  about  an  octave. 

There  is  no  solution  of  continuity  in  this  spectrum ; 
one  color  changes  into  another  by  insensible  gradations. 
It  is  as  if  an  infinite  number  of  tuning-forks,  of  gradually 
augmenting  pitch,  were  vibrating  at  the  same  time.  But 
turning  to  another  spectrum — that,  namely,  obtained  from 
the  incandescent  vapor  of  silver — you  observe  that  it  con- 
sists of  two  narrow  and  intensely  luminous  green  bands. 
Here  it  is  as  if  two  forks  only,  of  slightly  different  pitch, 
were  vibrating.  The  length  of  the  waves  which  produce 
this  first  band  is  such  that  47,460  of  them,  placed  end  to 
end,  would  fill  an  inch.  The  waves  which  produce  the 
second  band  are  a  little  shorter ;  it  would  take  of  these 
47,920  to  fill  an  inch.  In  the  case  of  the  first  band,  the 
number  of  impulses  imparted  in  one  second  to  every 
eye  which  now  sees  it,  is  577  millions  of  millions ;  while 
the  number  of  impulses  imparted  in  the  same  time  by  the 
second  band  is  600  millions  of  millions.  I  now  cast  upon 
-  the  screen  before  you  the  beautiful  stream  of  green  light 
from  which  these  bands  were  derived.  This  luminous 
stream  is  the  incandescent  vapor  of  silver.  The  rates  of 
vibration  of  the  atoms  of  that  vapor  are  as  rigidly  fixed  as 
those  of  two  tuning-forks;  and  to  whatever  height  the 
temperature  of  the  vapor  may  be  raised,  the  rapidity  of  its 
vibrations,  and  consequently  its  color,  which  wholly  de- 
pends upon  that  rapidity,  remains  unchanged. 

The  vapor  of  water,  as  well  as  the  vapor  of  silver,  has 
its  definite  periods  of  vibration,  and  these  are  such  as  to 
disqualify  the  vapor,  when  acting  freely  as  such,  from 
being  raised  to  a  white  heat.  The  oxyhydrogen  flame,  for 
example,  consists  of  hot  aqueous  vapor.  It  is  scarcely 
visible  in  the  air  of  this  room,  and  it  would  be  still  less 


RADIANT   HEAT  AND  ITS  RELATIONS.  219 

visible  if  we  could  burn  the  gas  in  a  clean  atmosphere. 
But  the  atmosphere,  even  at  the  summit  of  Mont  Blanc, 
is  dirty ;  in  London  it  is  more  than  dirty ;  and  the  burning 
dirt  gives  to  this  flame  the  greater  portion  of  its  present 
light.  But  the  heat  of  the  flame  is  enormous.  Cast-iron 
fuses  at  a  temperature  of  2,000°  Fahr.  A  piece  of  platinum 
is  heated  to  vivid  redness  at  a  distance  of  two  inches  be- 
yond the  visible  termination  of  the  flame.  The  vapor 
which  produces  incandescence  is  here  absolutely  dark.  In 
the  flame  itself  the  platinum  is  raised  to  dazzling  white- 
ness, and  is  finally  pierced  by  the  flame.  "When  this  flame 
impinges  on  a  piece  of  lime,  we  have  the  dazzling  Drum- 
mond  light.  But  the  light  is  here  due  to  the  fact  that 
when  it  impinges  upon  the  solid  body,  the  vibrations  ex- 
cited in  that  body  by  the  flame  are  of  periods  different  from 
its  own. 

Thus  far  we  have  fixed  our  attention  on  atoms  and 
molecules  in  a  state  of  vibration,  and  surrounded  by  a 
medium  which  accepts  their  vibrations,  and  transmits  them 
through  space.  But  suppose  the  waves  generated  by  one 
system  of  molecules  to  impinge  upon  another  system,  how 
will  the  waves  be  affected  ?  Will  they  be  stopped,  or  will 
they  be  permitted  to  pass  ?  Will  they  transfer  their  mo- 
tion to  the  molecules  on  which  they  impinge,  or  will  they 
glide  round  the  molecules,  through  the  intermolecular 
spaces,  and  thus  escape  ? 

The  answer  to  this  question  depends  upon  a  condition 
which  may  be  beautifully  exemplified  by  an  experiment  on 
sound.  These  two  tuning-forks  are  tuned  absolutely  alike. 
They  vibrate  with  the  same  rapidity,  and  mounted  thus 
upon  their  resonant  stands,  you  hear  them  loudly  sounding 
the  same  musical  note.  I  stop  one  of  the  forks,  and  throw 
the  other  into  strong  vibration.  I  now  bring  that  other 
near  the  silent  fork,  but  not  into  contact  with  it.  Allow- 
ing them  to  continue  in  this  position  for  four  or  five  seconds, 


220  FRAGMENTS  OF  SCIENCE. 

I  stop  the  vibrating  fork ;  but  the  sound  has  not  ceased. 
The  second  fork  has  taken  up  the  vibrations  of  its  neigh- 
bor, and  is  now  sounding  in  its  turn.  I  dismount  one  of 
the  forks,  and  permit  the  other  to  remain  upon  its  stand. 
I  throw  the  dismounted  fork  into  strong  vibration,  but  you 
cannot  hear  it  sound.  Detached  from  its  stand  the  amount 
of  motion  which  it  can  communicate  to  the  air  is  too  small 
to  make  itself  sensible  to  the  ear  at  any  distance.  I  now 
bring  the  dismounted  fork  close  to  the  mounted  one,  but 
not  into  actual  contact  with  it.  Out  of  the  silence  rises  a 
mellow  sound.  Whence  comes  it  ?  From  the  vibrations 
which  have  been  transferred  from  the  dismounted  fork  to 
the  mounted  one. 

That  motion  should  thus  transfer  itself  through  the  air 
it  is  necessary  that  the  two  forks  should  be  in  perfect  unison. 
If  I  place  on  one  of  the  forks  a  morsel  of  wax  not  larger 
than  a  pea,  it  is  rendered  thereby  powerless  to  affect,  or  to 
be  affected  by,  the  other.  It  is  easy  to  understand  this 
experiment.  The  pulses  of  the  one  fork  can  affect  the  other, 
because  they  are  perfectly  timed.  A  single  pulse  causes 
the  prong  of  the  silent  fork  to  vibrate  through  an  infinitesi- 
mal space.  But  just  as  it  has  completed  this  small  vibra- 
tion, another  pulse  is  ready  to  strike  it.  Thus,  the  small 
impulses  add  themselves  together.  In  the  five  seconds 
during  which  the  forks  were  held  near  each  other,  the  vi- 
brating fork  sent  1,280  waves  against  its  neighbor,  and 
those  1,280  shocks,  all  delivered  at  the  proper  moment,  all, 
as  I  have  said,  perfectly  timed,  have  given  such  strength 
to  the  vibrations  of  the  mounted  fork  as  to  render  them 
audible  to  you  all. 

Let  me  give  you  one  other  curious  illustration '  of  the 
influence  of  synchronism  on  musical  vibrations.  Here  are 
three  small  gas-flames  inserted  in  three  glass  tubes  of  dif- 
ferent lengths.  Each  of  these  flames  can  be  caused  to  emit 
a  musical  note,  the  pitch  of  which  is  determined  by  the 


RADIANT   HEAT  AND  ITS  RELATIONS.  221 

length  of  the  tube  surrounding  the  flame.  The  shorter  the 
tube  the  higher  is  the  pitch.  The  flames  are  now  silent 
within  their  respective  tubes,  but  each  of  them  can  be 
caused  to  respond  to  a  proper  note  sounded  anywhere  in 
this  room.  Here  is  an  instrument  called  a  siren,  by  which 
a  powerful  musical  note  can  be  produced.  Beginning  with 
a  note  of  low  pitch,  and  ascending  gradually  to  a  higher 
one,  I  finally  reach  the  note  of  the  flame  in  the  longest  tube. 
The  moment  it  is  reached,  the  flame  bursts  into  song.  But 
the  other  flames  are  still  silent  within  their  tubes.  I  urge 
the  instrument  on  to  higher  notes ;  the  second  flame  has 
now  started,  and  the  third  alone  remains.  But  a  still  higher 
note  starts  it  also.  Thus,  as  the  sound  of  the  siren  rises 
gradually  in  pitch,  it  awakens  every  flame  in  passing,  by 
striking  it  with  a  series  of  waves  whose  periods  of  recur- 
rence are  similar  to  its  own. 

Now  the  wave-motion  from  the  siren  is  in  part  taken  up 
by  the  flame  which  synchronizes  with  the  waves  ;  and  had 
these  waves  to  impinge  upon  a  multitude  of  flames,  instead 
of  upon  one  flame  only,  the  transference  might  be  so  great 
as  to  absorb  the  whole  of  the  original  wave-motion.  (JLet 
us  apply  these  facts  to  radiant  heat.  This  blue  flame  is 
the  flame  of  carbonic  oxide ;  this  transparent  gas  is  carbonic- 
acid  gas.  In  the  blue  flame  we  have  carbonic  acid  intensely 
heated ;  or,  in  other  words,  in  a  state  of  intense  vibration. 
It  thus  resembles  the  sounding  tuning-fork,  while  this  cold 
carbonic  acid  resembles  the  silent  one.  What  is  the  con- 
sequence ?  Through  the  synchronism  of  the  hot  and  cold 
gas  transmission  of  motion  through  the  gas  is  prevented ; 
it  is  all  transferred.  The  cold  gas  is  intensely  opaque  to 
the  radiation  from  this  particular  flame,  though  highly 
transparent  to  heat  of  every  other  kind.  We  are  here 
manifestly  dealing  with  that  great  principle  which  lies  at 
the  basis  of  spectrum  analysis,  and  which  has  enabled 
scientific  men  to  determine  the  substances  of  which  the  sun, 


222^  FRAGMENTS  OF  SCIENCE. 

the  stars,  and  even  the  nebulae,  are  composed  :  the  principle, 
namely,  that  a  body  which  is  competent  to  emit  any  ray, 
whether  of  heat  or  light,  is  competent  in  the  same  degree 
to  absorb  that  ray.  The  absorption  depends  on  the  syn- 
chronism which  exists  between  the  vibrations  of  the  atoms 
from  which  the  rays,  or  more  correctly  the  waves,  issue,  and 
those  of  the  atoms  against  which  they  impinge. 

To  its  incompetence  to  emit  white  light,  aqueous  vapor 
adds  incompetence  to  absorb  white  light.  It  cannot,  for 
example,  absorb  the  luminous  rays  of  the  sun,  though  it 
can  absorb  the  non-luminous  rays  of  the  earth.  This  in- 
competence of  aqueous  vapor  to  absorb  luminous  rays  is 
shared  by  water  and  ice — in  fact,  by  all  really  transparent 
substances.  Their  transparency  is  due  to  their  inability  to 
absorb  luminous  rays.  The  molecules  of  such  substances 
are  in  dissonance  with  the  luminous  waves,  and  hence  such 
waves  pass  through  transparent  substances  without  dis- 
turbing the  molecular  rest.  A  purely  luminous  beam,  how- 
ever intense  may  be  its  heat,  is  sensibly  incompetent  to 
melt  the  smallest  particle  of  ice.  We  can,  for  example, 
converge  a  powerful  luminous  beam  upon  a  surface  covered 
with  hoar-frost  without  melting  a  single  spicula  of  the  ice- 
crystals.  How  then,  it  may  be  asked,  are  the  snows  of  the 
Alps  swept  away  by  the  sunshine  of  summer  ?  I  answer 
they  are  not  swept  away  by  sunshine  at  all,  but  by  solar 
rays  which  have  no  sunshine  whatever  in  them.  The  lumi- 
nous rays  of  the  sun  fall  upon  the  snow-fields  and  are  flashed 
in  echoes  from  crystal  to  crystal,  but  they  find  next  to  no 
lodgment  within  the  crystals.  They  are  hardly  at  all  ab- 
sorbed, and  hence  they  cannot  produce  fusion.  But  a  body 
of  powerful  dark  rays  is  emitted  by  the  sun,  and  it  is  these 
rays  that  cause  the  glaciers  to  shrink  and  the  snows  to  dis- 
appear ;  it  is  they  that  fill  the  banks  of  the  Arve  and  Ar- 
veyron,  and  liberate  from  their  frozen  captivity  the  Rhone 
and  the  Rhine. 


RADIANT  HEAT  AND  ITS  RELATIONS.  223 

Placing  a  concave  silvered  mirror  behind  the  electric 
light  I  converge  its  rays  to  a  focus  of  dazzling  brilliancy. 
I  place  in  the  path  of  the  rays,  between  the  light  and  the 
focus,  a  vessel  of  water,  and  now  introduce  at  the  focus  a 
piece  of  ice.  The  ice  is  not  melted  by  the  concentrated 
beam  which  has  passed  through  the  water,  though  matches 
are  ignited  at  the  focus  and  wood  is  set  on  fire.  The  pow- 
erful heat,  then,  of  this  luminous  beam  is  incompetent  to 
melt  the  ice.  I  withdraw  the  cell  of  water ;  the  ice  imme- 
diately liquefies,  and  you  see  the  water  trickling  from  it 
in  drops.  I  reintroduce  the  cell  of  water;  the  fusion  is 
arrested  and  the  drops  cease  to  fall.  The  transparent  water 
of  the  cell  exerts  no  sensible  absorption  on  the  luminous 
rays,  still  it  withdraws  something  from  the  beam,  which, 
when  permitted  to  act,  is  competent  to  melt  the  ice.  This 
something  is  the  dark  radiation  of  the  electric  light.  Again, 
I  place  a  slab  of  pure  ice  in  front  of  the  electric  lamp  ;  send 
a  luminous  beam  first  through  our  cell  of  water  and  then 
through  the  ice.  By  means  of  a  lens  an  image  of  the  slab 
is  cast  upon  a  white  screen.  The  beam,  sifted  by  the  water, 
has  no  power  upon  the  ice.  But  observe  what  occurs  when 
the  water  is  removed ;  we  have  here  a  star  and  there  a  star, 
each  star  resembling  a  flower  of  six  petals,  and  growing 
visibly  larger  before  our  eyes.  As  the  leaves  enlarge  their 
edges  become  serrated,  but  there  is  no  deviation  from  the 
six-rayed  type.  We  have  here,  in  fact,  the  crystallization 
of  the  ice  inverted  by  the  invisible  rays  of  the  electric  beam. 
They  take  the  molecules  down  in  this  wonderful  way,  and 
reveal  to  us  the  exquisite  atomic  structure  of  the  substance 
with  which  Nature  every  winter  roofs  our  ponds  and  lakes. 

Numberless  effects,  apparently  anomalous,  might  be  ad- 
duced in  illustration  of  the  action  of  these  lightless  rays. 
Here,  for  example,  are  two  powders,  both  white,  and  undis- 
tinguishable  from  each  other  by  the  eye.  The  luminous 
rays  of  the  lamp  are  unabsorbed  by  both  powders — from 


224  FRAGMENTS  OF  SCIENCE. 

those  rays  they  acquire  no  heat ;  still  one  of  the  substances, 
sugar,  is  heated  so  highly  by  the  concentrated  beam  of  the 
electric  lamp  that  it  first  smokes  violently  and  then  inflames, 
while  the  other  substance,  salt,  is  barely  warmed  at  the 
focus.  Here,  again,  are  two  perfectly  transparent  liquids 
placed  in  a  test-tube  at  the  focus ;  one  of  them  boils  in  a 
couple  of  seconds,  while  the  other  in  a  similar  position  is 
hardly  warmed.  The  boiling-point  of  the  first  liquid  is  78° 
C.,  which  is  speedily  reached;  that  of  the  second  liquid  is 
only  48°  C.,  which  is  never  reached  at  all.  These  anoma- 
lies are  entirely  due  to  the  unseen  element  which  mingles 
with  the  luminous  rays  of  the  electric  beam,  and,  indeed, 
constitutes  90  per  cent,  of  its  calorific  power. 

I  have  here  a  substance  by  which  these  dark  rays  may 
be  detached  from  the  total  emission  of  the  electric  lamp. 
This  ray-filter  is  a  black  liquid — that  is  to  say,  black  as 
pitch  to  the  luminous,  but  bright  as  a  diamond  to  the  non- 
luminous  radiation.  It  mercilessly  cuts  off  the  former,  but 
allows  the  latter  free  transmission.  I  bring  these  invisible 
rays  to  a  focus  at  a  distance  of  several  feet  frcm  the  electric 
lamp ;  the  dark  rays  form  there  an  invisible  image  of  the 
source  from  which  they  issue.  By  proper  means  this  in- 
visible image  may  be  transformed  into  a  visible  one  of  'daz- 
zling brightness.  I  could,  moreover,  show  you,  if  .time  per- 
mitted, how  out  of  those  perfectly  dark  rays  we  might  ex- 
tract, by  a  process  of  transmutation,  all  the  colors  of  the 
solar  spectrum.  I  could  also  prove  to  you  that  those  rays, 
powerful  as  they  are,  and  sufficient  to  fuse  many  metals, 
may  be  permitted  to  enter  the  eye  and  to  break  upon  the 
retina  without  producing  the  least  luminous  impression. 

The  dark  rays  are  now  collected  before  you ;  you  see 
nothing  at  their  place  of  convergence ;  with  a  proper  ther- 
mometer it  could  be  proved  that  even  the  air  at  the  focus 
is  just  as  cold  as  the  surrounding  air.  And  mark  the  con- 
clusion to  which  this  leads'.  It  proves  the  ether  at  the  focus 


RADIANT  HEAT  AND  ITS  RELATIONS.  225 

to  be  practically  detached  from  the  air — that  the  most  vio- 
lent ethereal  motion  may  there  exist  without  the  least 
aerial  motion.  But  though  you  see  it  not,  there  is  suffi- 
cient heat  at  that  focus  to  set  London  on  fire.  The  heat 
there  at  the  present,  moment  is  competent  to  raise  iron  to  a 
temperature  at  which  it  throws  off  brilliant  scintillations. 
It  can  heat  platinum  to  whiteness  and  almost  fuse  that  re- 
fractory metal.  It  actually  can  fuse  gold,  silver,  copper, 
and  aluminium.  The  moment,  moreover,  that  wood  is 
placed  at  the  focus  it  bursts  into  a  blaze. 

It  has  been  already  affirmed  that  whether  as  regards  ra- 
diation or  absorption  the  elementary  atoms  possess  but  little 
power.  This  might  be  illustrated  by  a  long  array  of  facts  ; 
and  one  of  the  most  singular  of  these  is  furnished  by  the 
deportment  of  that  extremely  combustible  substance,  phos- 
phorus, when  placed  at  this  dark  focus.  It  is  impossible  to 
ignite  there  a  fragment  of  amorphous  phosphorus.  But  or- 
dinary phosphorus  is  a  far  quicker  combustible,  and  its  de- 
portment to  radiant  heat  is  still  more  impressive.  It  may 
be  exposed  to  the  intense  radiation  of  an  ordinary  fire  with- 
out bursting  into  flame.  It  may  also  be  exposed  for  twenty 
or  thirty  seconds  at  an  obscure  focus  of  sufficient  power  to 
raise  platinum  to  a  white  heat,  without  ignition.  Notwith- 
standing the  energy  of  the  ethereal  waves  here  concentrated, 
notwithstanding  the  extremely  inflammable  character  of 
the  elementary  body  exposed  to  their  action,  the  atoms  of 
that  body  refuse  to  partake  of  the  motion  of  the  waves,  and 
consequently  cannot  be  powerfully  affected  by  their  heat. 

The  knowledge  which  we  now  possess  will  enable  us  to 
analyze  with  profit  a  practical  question.  White  dresses  are 
worn  in  summer  because  they  are  found  to  be  cooler  than 
dark  ones.  The  celebrated  Benjamin  Franklin  made  the  fol- 
lowing experiment:  He  placed  bits  of  cloth  of  various  colors 
upon  snow,  exposed  them  to  direct  sunshine,  and  found  that 
they  sank  to  different  depths  in  the  snow.  The  black  cloth 


226  FRAGMENTS  OF  SCIENCE. 

sank  the  deepest,  the  white  did  not  sink  at  all.  Franklin 
inferred  from  his  experiment  that  black  bodies  are  the  best 
absorbers,  and  white  ones  the  worst  absorbers,  of  radiant 
heat.  Let  us  test  the  generality  of  this  conclusion.  I  have 
here  two  cards,  one  of  which  is  coated  with  a  very  dark 
powder,  and  the  other  with  a  perfectly  white  one.  I  place 
the  powdered  surfaces  before  the  fire,  and  leave  them  there 
until  they  have  acquired  as  high  a  temperature  as  they  can 
attain  in  this  position.  Which  of  the  cards  is  most  highly* 
heated  ?  It  requires  no  thermometer  to  answer  this  ques- 
tion ?  Simply  pressing  the  back  of  the  card,  on  wrhich  the 
white  powder  is  strewn,  against  my  cheek  or  forehead,  I 
find  it  intolerably  hot.  Placipg  the  dark  card  in  the  same 
position  I  find  it  cool.  The  white  powder  has  absorbed  far 
more  heat  than  the  dark  one.  This  simple  result  abolishes 
a  hundred  conclusions  which  have  been  hastily  drawn  from 
the  experiment  of  Franklin.  Again,  here  are  suspended 
two  delicate  mercurial  thermometers  at  the  same  distance 
from  a  gas-flame.  The  bulb  of  one  of  them  is  covered  by  a 
dark  substance,  the  bulb  of  the  other  by  a  white  one.  Both 
bulbs  have  received  the  radiation  from  the  flame,  but  the 
white  bulb  has  absorbed  most,  and  its  mercury  stands  much 
higher  than  that  of  the  other  thermometer.  I  might  vary 
this  experiment  in  a  hundred  ways,  and  show  you  that  from 
the  darkness  of  a  body  you  can  draw  no  certain  conclusion 
regarding  its  power  of  absorption. 

The  reason  of  this  simply  is,  that  color  gives  us  intelli- 
gence of  only  one  portion,  and  that  the  smallest  one,  of 
the  rays  impinging  on  the  colored  body.  Were  the  rays 
all  luminous  we  might  with  certainty  infer  from  the  color 
of  a  body  its  power  of  absorption  ;  but  the  great  mass  of 
the  radiation  from  our  fire,  our  gas-flame,  and  even  from 
the  sun  itself,  consists  of  invisible  calorific  rays,  regarding 
which  color  teaches  us  nothing.  A  body  may  be  highly  trans- 
parent to  one  class  of  rays,  and  highly  opaque  to  the  other 


RADIANT  HEAT  AND  ITS  RELATIONS.  227     ' 

class.  Thus  the  white  powder,  which  has  shown  itself  so 
powerful  an  absorber,  has  been  specially  selected  on  account 
of  its  extreme  perviousness  to  the  visible  rays,  and  its  ex- 
treme imperviousness  to  the  invisible  ones  ;  while  the  dark 
powder  was  chosen  on  account  of  its  extreme  transparency 
to  the  invisible,  and  its  extreme  opacity  to  the  visible  rays. 
In  the  case  of  the  radiation  from  our  fire,  about  98  per  cent, 
of  the  whole  emission  consists  of  invisible  rays ;  the  body, 
therefore,  which  was  most  opaque  to  these  triumphed  as 
an  absorber,  though  that  body  was  a  white  one.  ^ 

I  would  here  invite  you  to  consider  the  manner  in 
which  we  obtain  from  natural  facts  what  may  be  called 
their  intellectual  value.  Throughout  the  processes  of  Na- 
ture there  is  interdependence  and  harmony,  and  the  main 
value  of  our  science,  considered  as  a  mental  discipline,  con-  / 
sists  in  the  tracing  of  this  interdependence  and  the  demon- 
stration of  this  harmony.  The  outward  and  visible  phe- 
nomena are  with  us  the  counters  of  the  intellect ;  and  our 
science  would  not  be  worthy  of  its  name  and  fame  if  it 
halted  at  facts,  however  practically  useful,  and  neglected 
the  laws  which  accompany  and  rule  phenomena.  Let  us 
endeavor,  then,  to  extract  from  the  experiment  of  Franklin 
its  full  intellectual  value,  calling  to  our  aid  the  knowledge 
which  our  predecessors  have  already  stored.  Let  us  im- 
agine two  pieces  of  cloth  of  the  same  texture,  the  one 
black  and  the  other  white,  placed  upon  sunned  snow.  Fix- 
ing our  attention  on  the  white  piece,  let  us  inquire  whether 
there  is  any  reason  to  expect  that  it  will  sink  into  the 
snow  at  all.  There  is  knowledge  at  hand  which  enables 
us  to  reply  at  once  in  the  negative.  There  is,  on  the  con- 
trary, reason  to  expect  that  after  a  sufficient  exposure  the 
bit  of  cloth  will  be  found  on  an  eminence  instead  of  in  a 
hollow ;  that  instead  of  a  depression,  we  shall  have  a  rela- 
tive elevation  of  the  bit  of  cloth.  For,  as  regards  the  lu- 
minous rays  of  the  sun,  the  cloth  and  the  snow  are  alike 


228  FRAGMENTS  OF  SCIENCE. 

powerless;  the  one  cannot  be  warmed,  nor  the  other 
melted,  by  such  rays.  The  cloth  is  white  and  the  snow  is 
white,  because  then:  confusedly  mingled  particles  and  fibres 
are  incompetent  to  absorb  luminous  rays.  Whether,  then, 
the  cloth  will  sink  or  not  depends  entirely  upon  the  dark 
rays  of  the  sun.  Now  the  substance  which  absorbs  the 
dark  rays  of  the  sun  with  the  greatest  avidity  is  ice — or 
snow,  which  is  merely  ice  in  powder.  A  less  amount  of 
heat  will  be  lodged  in  the  cloth  than  in  the  surrounding 
snow.  The  cloth  must,  therefore,  act  as  a  shield  to  the 
snow  on  which  it  rests ;  and  in  consequence  of  the  more 
rapid  fusion  of  the  exposed  snow,  the  cloth  must  in  due 
time  be  left  behind,  perched  upon  an  eminence  like  a  gla- 
cier-table. 

But  though  the  snow  transcends  the  cloth  both  as  a 
radiator  and  absorber,  it  does  not  much  transcend  it. 
Cloth  is  very  powerful  in  both  these  respects.  Let  us 
now  turn  our  attention  to  the  piece  of  black  cloth,'  the 
texture  and  fabric  of  which  I  assume  to  be  ther  same  as 
that  of  the  white.  For  our  object  being  to  compare  the 
effects  of  color,  we  must,  in  order  to  study  this  effect  in  its 
purity,  preserve  all  other  conditions  constant.  Let  us  then 
suppose  the  black  cloth  to  be  obtained  from  the  dyeing 
of  the  white.  The  cloth  itself,  without  reference  to  the 
dye,  is  nearly  as  good  an  absorber  of  heat  as  the  snow 
around  it.  But  to  the  absorption  of  the  dark  solar  rays 
by  the  undyed  cloth  is  now  added  the  absorption  of  the 
whole  of  the  luminous  rays,  and  this  great  additional  in- 
flux of  heat  is  far  more  than  sufficient  to  turn  the  balance 
in  favor  of  the  black  cloth.  The  sum  of  its  actions  on  the 
dark  and  luminous  rays  exceeds  the  action  of  the  snow 
on  the  dark  rays  alone.  Hence  the  cloth  will  sink  in  the 
snow,  and  this  is  the  philosophy  of  Franklin's  experi- 
ment. 

Throughout  this  discourse  the  main  stress  has  been  laid 


RADIANT  HEAT  AND  ITS  RELATIONS.  229 

on  chemical  constitution,  as  influencing  most  powerfully 
the  phenomena  of  radiation  and  absorption.  With  regard 
to  gases,  vapors,  and  to  the  liquids  from  which  these  va- 
pors are  derived,  it  has  been  proved  by  the  most  varied 
and  conclusive  experiments  that  the  acts  of  radiation  and 
absorption  are  molecular — that  they  depend  upon  chemical 
and  not  upon  mechanical  condition.  In  attempting  to  ex- 
tend this  principle  to  solids  I  was  met  by  a  multitude  of 
facts  obtained  by  celebrated  experimenters,  which  seemed 
flatly  to  forbid  such  extension.  Melloni,  for  example,  found 
the  same  radiant  and  absorbent  power  for  chalk  and  lamp- 
black. MM.  Masson  and  Courtepee  performed  a  most 
elaborate  series  of  experiments  on  chemical  precipitates  of 
various  kinds,  and  found  that  they  one  and  all  manifested 
the  same  power  of  radiation.  They  concluded  from  their 
researches,  that  where  bodies  are  reduced  to  an  extremely 
fine  state  of  division  the  influence  of  this  state  is  so  power- 
ful as  entirely  to  mask  and  override  whatever  influence 
may  be  due  to  chemical  constitution. 

But  it  appears  to  me  that  through  the  whole  of  these 
researches  a  serious  oversight  has  run,  the  mere  mention 
of  which  will  show  you  what  caution  is  essential  in  the 
operations  of  experimental  philosophy.  Let  me  state 
wherein  I  suppose  this  oversight  to  consist.  I  have  here 
a  metal  cube  with  two  of  its  sides  brightly  polished.  I 
fill  the  cube  with  boiling  water  and  determine  the  quan- 
tity of  heat  emitted  by  the  two  bright  surfaces.  One  of 
them  far  transcends  the  other  as  a  radiator  of  heat.  Both 
surfaces  appear  to  be  metallic ;  what,  then,  is  the  cause  of 
the  observed  difference  in  their  radiative  power  ?  Simply 
this:  I  have  coated,  one  of  the  surfaces  with  transparent 
gum,  through  which,  of  course,  is  seen  the  metallic  lustre 
behind.  Now  this  varnish,  though  so  perfectly  transparent 
to  luminous  rays,  is  as  opaque  as  pitch  or  lamp-black  to 
non-luminous  ones.  It  is  a  powerful  emitter  of  dark  rays ; 


230  FRAGMENTS  OF  SCIENCE. 

it  is  also  a  powerful  absorber.  While,  therefore,  at  the 
present  moment  it  is  copiously  pouring  forth  radiant  heat 
itself,  it  does  not  allow  a  single  ray  from  the  metal  behind 
to  pass  through  it.  The  varnish  then,  and  not  the  metal,  is 
the  real  radiator. 

Now  Melloni,  and  Masson,  and  Courtepee,  experimented 
thus:  they  mixed  their  powders  and  precipitates  with 
gum-water,  and  laid  them  by  means  of  a  brush  upon  the 
surfaces  of  a  cube  like  this.  True  they  saw  their  red  pow- 
ders red,  their  white  ones  white,  and  their  black  ones  black, 
but  they  saw  these  colors  through  the  coat  of  varnish 
which  encircled  every  particle  of  their  powders.  When, 
therefore,  it  was  concluded  that  color  had  no  influence  on 
radiation,  no  chance  had  been  given  to  it  of  asserting  its 
influence ;  when  it  was  found  that  all  chemical  precipitates 
radiated  alike,  it  was  the  radiation  from  a  varnish  common 
to  them  all  which  showed  the  observed  constancy.  Hun- 
dreds, perhaps  thousands,  of  experiments  on  radiant  heat 
have  been  performed  in  this  way  by  various  inquirers,  but 
I  fear  the  work  will  have  to  be  done  over  again.  I  am  not, 
indeed,  acquainted  with  an  instance  in  which  an  oversight 
of  so  trivial  a  character  has  been  committed  in  succession 
by  so  many  able  men,  and  vitiated  so  large  an  amount  of 
otherwise  excellent  work. 

Basing  our  reasonings,  then,  on  demonstrated  facts,  we 
arrive  at  the  extremely  probable  conclusion  that  the  envel- 
ope of  the  particles,  and  not  the  particles  themselves,  was 
the  real  radiator  in  the  experiments  just  referred  to.  To 
reason  thus,  and  deduce  their  more  or  less  probable  conse- 
quences from  experimental  facts,  is  an  incessant  exercise 
of  the  student  of  physical  science.  But  having  thus  fol- 
lowed for  a  time  the  light  of  reason  alone  through  a  series 
of  phenomena,  and  emerged  from  them  with  a  purely  intel- 
lectual conclusion,  our  duty  is  to  bring  that  conclusion  to 
an  experimental  test.  In  this  way  we  fortify  our  science, 


KADIANT   HEAT  AND   ITS  RELATIONS.  231 

sparing  no  pains,  shirking  no  toil  to  secure  sound  materials 
for  the  edifice  which  it  is  our  privilege  to  raise. 

For  the  purpose  of  testing  our  conclusion  regarding  the 
influence  of  the  gum  I  take  two  powders  of  the  same  physi- 
cal appearance ;  one  of  them  is  a  compound  of  mercury  and 
the  other  a  compound  of  lead.  On  two  surfaces  of  this 
cube  are  spread  these  bright-red  powders  without  varnish 
of  any  kind.  Filling  the  tube  with  boiling  water,  and  de- 
termining the  radiation  from  the  two  surfaces,  one  of  them 
is  found  to  emit  thirty-nine  rays,  while  the  other  emits 
seventy-four.  This,  surely,  is  a  great  difference.  Here, 
however,  is  a  second  cube,  having  two  of  its  surfaces  coated 
with  the  same  powders,  the  only  difference  being  that  now 
the  powders  are  laid  on  by  means  of  a  transparent  gum. 
Both  surfaces  are  now  absolutely  alike  in  radiative  power. 
Both  of  them  emit  somewhat  more  than  was  emitted  by 
either  of  the  unvarnished  powders,  simply  because  the  gum 
employed  is  a  better  radiator  than  either  of  them.  Exclud- 
ing all  varnish,  and  comparing  white  with  white,  I  find 
vast  differences  ;  comparing  black  with  black,  I  find  them 
also  different;  and  when  black  and  white  are  compared,  in 
some  cases  the  black  radiates  far  more  than  the  white, 
while  in  other  cases  the  white  radiates  far  more  than  the 
black.  Determining,  moreover,  the  absorptive  power  of 
those  powders,  it  is  found  to  go  hand-in-hand  with  their 
radiative  power.  The  good  radiator  is  a  good  absorber,  and 
the  bad  radiator  is  a  bad  absorber.  From  all  this  it  is  evi- 
dent that  as  regards  the  radiation  and  absorption  of  non- 
luminous  heat,  color  teaches  us  nothing ;  and  that  even  as 
regards  the  radiation  of  the  sun,  consisting  as  it  does  main- 
ly of  non-luminous  rays,  conclusions  as  to  the  influence  of 
color  may  be  altogether  delusive.  This  is  the  strict  scien- 
tific upshot  of  our  researches.  But  it  is  not  the  less  true 
that  in  the  case  of  wearing  apparel — and  this  for  reasons 
which  I  have  given  in  analyzing  the  experiment  of  Frank- 


232  FRAGMENTS  OF  SCIENCE. 

lin — black  dresses  are  more  potent  than  white  ones  as  ab- 
sorbers of  solar  heat. 

Thus,  in  brief  outline,  I  have  brought  before  you  a  few 
of  the  results  of  recent  inquiry.  If  you  ask  me  what  is  the 
use  of  them,  I  can  hardly  answer  you,  unless  you  define  the 
term  use.  If  you  meant  to  ask  me  whether  those  dark 
rays  which  clear  away  the  Alpine  snows  will  ever  be  ap- 
plied to  the  roasting  of  turkeys  or  the  driving  of  steam- 
engines,  while  affirming  their  power  to  do  both,  I  would 
frankly  confess  that  they  are  not  at  present  capable  of 
competing  profitably  with  coal  in  these  particulars.  Still 
they  may  have  great  uses  unknown  to  me ;  and  when  our 
coal-fields  are  exhausted,  it  is  possible  that  a  more  ethereal 
race  than  ourselves  may  cook  their  victuals  and  perform 
their  work  in  this  transcendental  way.  But  is  it  necessary 
that  the  student  of  science  should  have  his  labors  tested  by 
their  possible  practical  applications  ?  What  is  the  prac- 
tical value  of  Homer's  Iliad?  You  smile,  and  possibly 
think  that  Homer's  Iliad  is  good  as  a  means  of  culture. 
There's  the  rub.  The  people  who  demand  of  science  prac- 
tical uses,  forget,  or  do  not  know,  that  it  also  is  great  as  a 
means  of  culture ;  that  the  knowledge  of  this  wonderful 
universe  is  a  thing  profitable  in  itself,  and  requiring  no 
practical  application  to  justify  its  pursuit.  But  while  the 
student  of  Nature  distinctly  refuses  to  have  his  labors 
judged  by  their  practical  issues,  unless  the  term  practical 
be  made  to  include  mental  as  well  as  material  good,  he 
knows  full  well  that  the  greatest  practical  triumphs  have 
been  episodes  in  the  search  after  pure  natural  truth.  The 
electric  telegraph  is  the  standing  wonder  of  this  age,  and 
the  men  whose  scientific  knowledge  and  mechanical  skill 
have  made  the  telegraph  what  it  is  are  deserving  of  all 
honor.  In  fact,  they  have  their  reward,  both  in  reputation 
and  in  those  more  substantial  benefits  which  the  direct  ser- 
vice of  the  public  always  carries  in  its  train.  But  who,  I 


RADIANT  HEAT  AND   ITS  RELATIONS.  233 

would  ask,  put  the  soul  into  this  telegraphic  body  ?  Who 
snatched  from  heaven  the  fire  that  flashes  along  the  line  ? 
This,  I  am  bound  to  say,  was  done  by  two  men,  the  one  a 
dweller  in  Italy,1  the  other  a  dweller  in  England,  and,  there- 
fore, not  a  thousand  miles  distant  from  the  spot  where  I 
now  stand,2  who  never  in  their  inquiries  consciously  set  a 
practical  object  before  them  —  whose  only  stimulus  was 
the  fascination  which  draws  the  climber  to  a  never-trodden 
peak,  and  would  have  made  Csesar  quit  his  victories  to 
seek  the  sources  of  the  Nile.  That  the  knowledge  brought 
us  by  those  prophets,  priests,  and  kings  of  science,  is  what 
the  world  calls  useful  knowledge,  the  triumphant  applica- 
tion of  their  discoveries  proves.  But  science  has  another 
function  to  fulfil,  in  the  storing  and  the  training  of  the  hu- 
man mind ;  and  I  would  base  my  appeal  to  you  on  the 
poor  specimen  which  has  been  brought  before  you  this 
evening,  whether  any  system  of  education  at  the  present 
day  can  be  deemed  even  approximately  complete  in  which 
the  knowledge  of  Nature  is  neglected  or  ignored. 

1  Volta.  2  Faraday. 


X. 

ON  CHEMICAL  RAYS  AND  THE  STRUCT- 
URE AND  LIGHT  OF  THE  SKY. 

A  DISCOURSE. 

DELIVERED  IN  THE  ROYAL  INSTITUTION  OF  GREAT  BEITAIN. 
On  Friday,  January  15, 1869. 


"  This  is  a  very  mysterious  and  a  very  beautiful  phenomenon  when 
observed  by  the  aid  of  a  polariscope,  consisting  of  a  tourmaline  plate, 
with  a  slice  of  Iceland  crystal  or  nitre,  cut  at  right  angles  to  the  optic 
axis,  and  applied  on  the  side  of  the  tourmaline  farthest  from  the  eye.  In 
a  cloudless  day,  if  the  sky  be  explored  in  all  parts  by  looking  through 
this  compound  plate,  the  polarized  rings  will  be  seen  developed  with  more 
or  less  intensity  in  every  region  but  that  nearest  the  sun  and  that  most 
distant  from  it — the  maximum  of  polarization  taking  place  on  a  zone  of 
the  sky  90°  from  the  sun,  or  in  a  great  circle,  having  the  sun  for  one  of 
its  poles,  so  that  the  cause  of  polarization  is  evidently  a  reflection  of  the 
sun's  light  on  something.  The  question  is,  on  what  ?  Were  the  angle  of 
maximum  polarization  76°  we  should  look  to  water  or  ice  for  the  reflect- 
ing body.  But  though  we  were  once  of  this  opinion  (art.  Light,  Encycl. 
Metropol.  §  1143),  careful  observation  has  satisfied  us  that  90°,  or  there- 
abouts, is  the  correct  angle,  and  that  therefore,  whatever  be  the  body  on 
which  the  light  has  been  reflected,  if  polarized  by  a  single  reflection,  the 
c  polarizing  angle '  must  be  45°,  and  the  index  of  refraction,  which  is  the 
tangent  of  that  angle,  unity ;  in  other  words,  the  reflection  would  require 
to  be  made  in  air  upon  air  !  The  only  imaginable  way  in  which  this  could 
happen  would  be  at  the  plane  of  contact  of  two  portions  of  air  differently 
heated,  such  as  might  be  supposed  to  occur  at  almost  every  point  of  the 
atmosphere  in  a  bright  sunny  day  ;  but  against  this  there  seems  to  be  an 
insuperable  objection.  The  polarization  is  most  regular  and  complete,  as 
we  have  lately  been  able  to  satisfy  ourselves  under  the  most  favorable 
possible  atmospheric  conditions,  after  sunset,  in  the  bright  twilight  of  a 
summer  night,  with  the  sun  some  degrees  below  the  horizon,  and  long 
after  all  the  tremor  and  turmoil  of  the  air,  due  to  irregular  heating,  must 
have  completely  subsided.  On  the  other  hand,  if  effected  by  several  suc- 
cessive reflections,  what  is  to  secure  a  large  majority  of  them  being  in 
one  plane  (in  which  case  only  their  polarizing  effect  would  accumulate) ; 
and  of  those  which  become  ultimately  effective,  what,  is  there  to  deter- 
mine an  ultimate  deviation  of  90°  as  that  of  the  maximum  ?  The  more 
the  subject  is  considered,  the  more  it  will  be  found  beset  with  difficulties ; 
and  its  explanation,  when  arrived  at,  will  probably  be  found  to  carry 
with  it  that  of  the  blue  color  of  the  sky  itself." 

SIR  JOHN  HERSCHEL. 


X. 


ON   CHEMICAL  BAYS  AND   THE.   STRUCTURE  AND 
LIGHT  OF  THE  SKY. 

THE  first  physical  investigation  of  any  importance  in 
which,  jointly  with  my  friend  Professor  Knoblauch,  I  took 
part,  bore  the  title :  "  The  Magneto-optic  Properties  of 
Crystals,  and  the  Relation  of  Magnetism  and  Diamagnetism 
to  Molecular  Arrangement."  1  This  investigation  compelled 
me  to  reflect  upon  the  structure  of  crystals,  on  their  optical 
properties  in  relation  to  that  structure,  and  more  particu- 
larly on  the  striking  phenomena  exhibited  by  many  of 
them  in  the  field  of  a  sufficiently  powerful  magnet.  These 
were  evidently  due  to  the  manner  in  which  the  molecules 
of  the  crystals  were  built  together  by  the  force  of-  crystal- 
lization ;  and  it  was  natural,  if  not  necessary  for  me,  to  em- 
ploy such  strength  of  imagination  as  I  possessed  in  obtain- 
ing a  mental  picture  of  this  molecular  architecture.  The 
inquiry  gave  a  tinge  and  bias  to  my  subsequent  scientific 
thought,  rendering,  as  it  did,  the  conceptions  and  pursuits 
of  molecular  physics  pleasant  to  me.  Its  influence  is  to  be 
traced  in  most  of  my  scientific  work.  The  first  lecture,  for 
example,  which  I  ever  delivered  in  this  theatre,  was  "  On 
the  Influence  of  Material  Aggregation  on  the  Manifestations 
of  Force  ;  "  by  "  material  aggregation  "  being  meant  the 
way  in  which,  by  Nature  or  by  Art,  the  molecules  of  mat- 

1  Philosophical  Magazine,  July,  1850. 


238  FKAGMENTS  OF  SCIENCE. 

ter  are  arranged  together.  In  1853  I  also  published  a 
paper  "  On  Molecular  Influences,"  in  which  common  heat 
was  made  the  explorer  of  organic  structure.  In  the  "  Ba- 
kerian  Lecture,"  given  before  the  Royal  Society  in  1855, 
the  same  idea  and  phraseology  crop  out.  The  Bakerian 
Lecture  for  1864  bears  the  title  "  Contributions  to  Molec- 
ular Physics."  And  all  through  the  investigations  which 
have  occupied  me  during  the  last  ten  years,  my  wish  and 
aim  have  been  to  make  radiant  heat  an  instrument  by 
which  to  lay  hold  of  the  ultimate  particles  of  matter. 

The  labors  now  to  be  considered  lie  in  the  same  direc- 
tion. In  the  researches  just  referred  to,  tubes  of  glass  and 
brass  were  employed,  called,  for  the  sake  of  distinction, 
"  experimental  tubes,"  in  which  radiant  heat  was  acted 
upon  by  the  gases  and  vapors  subjected  to  examination. 
Two  or  three  months  ago,  with  a  view  of  seeing  what  oc- 
curred within  these  tubes  on  the  entrance  of  the  gases  or 
vapors,  it  was  found  necessary  to  intensely  illuminate  their 
interiors.  The  source  of  illumination  chosen  was  the  elec- 
tric light,  the  beam  of  which,  converged  by  a  suitable  lens, 
was  sent  along  the  axis  of  the  tube.  The  dirt  and  filth  in 
which  we  habitually  live  were  strikingly  revealed  by  this 
method  'of  illumination.  For,  wash  the  tube  as  we  might 
with  water,  alcohol,  acid,  or  alkali,  until  its  appearance  in 
ordinary  daylight  was  that  of  absolute  purity,  the  delusive 
character  of  this  appearance  was  in  most  cases  revealed  by 
the  electric  beam.  In  fact,  in  air  so  charged  with  sus- 
pended matter  as  that  which  supplies  our  lungs  in  London, 
it  is  not  possible  to  be  more  than  approximately  clean. 

Vapors  of  various  kinds  were  sent  into  a  glass  experi- 
mental tube,  a  yard  in  length,  and  about  three  inches  in 
diameter.  As  a  general  rule,  the  vapors  were  perfectly 
transparent ;  the  tube,  when  they  were  present,  appearing 
as  empty  as  when  they  were  absent.  In  two  or  three  cases, 
however,  a  faint  cloudiness  showed  itself  within  the  tube. 


CHEMICAL  RAYS.  239 

This  caused  me  a  momentary  anxiety,  for  I  did  not  know 
how  far,  in  describing  my  previous  experiments,  actions 
might  have  been  ascribed  to  pure  cloudless  vapor,  which 
were  really  due  to  those  newly-observed  nebulas.  Inter- 
mittent discomfort,  however,  is  the  normal  feeling  of  the 
investigator ;  for  it  drives  him  to  closer  scrutiny,  to  greater 
accuracy,  and  often,  as  a  consequence,  to  new  discovery. 
It  was  soon  found  that  the  nebulae  revealed  by  the  beam 
were  also  generated  by  the  beam,  and  the  observation 
opened  a  new  door  into  that  region  inaccessible  to  sense, 
which  embraces  so  much  of  the  intellectual  life  of  the  phys- 
ical investigator. 

"What  are  those  vapors  of  which  we  have  been  speak- 
ing ?  They  are  aggregates  of  molecules^  or  small  masses  of 
matter,  and  every  molecule  is  itself  an  aggregate  of  smaller 
parts  called  atoms.  A  molecule  of  aqueous  vapor,  for  ex- 
ample, consists  of  two  atoms  of  hydrogen  and  one  of  oxy- 
gen. A  molecule  of  ammonia  consists  of  three  atoms  of 
hydrogen,  and  one  of  nitrogen,  and  so  of  other  substances. 
Thus  the  molecules,  themselves  inconceivably  small,  are 
made  up  of  distinct  parts  still  smaller.  When,  therefore, 
a  compound  vapor  is  spoken  of,  the  corresponding  mental 
image  is  an  aggregate  of  molecules  separated  from  each 
other,  though  still  exceedingly  near,  each  of  these  being 
composed  of  a  group  of  atoms  still  nearer  to  each  other. 
So  much  for  the  matter  which  enters  into  our  conception  of 
a  vapor.1  To  this  must  now  be  added  the  idea  of  motion. 
The  molecules  have  motions  of  their  own  as  wholes  y  their 
constituent  atoms  have  also  motions  of  their  own,  which 
are  executed  independently  of  those  of  the  molecules  ;  just 

1  Newton  seemed  to  consider  that  the  molecules  might  be  rendered 
visible  by  microscopes  ;  but  of  the  atoms  he  appears  to  have  entertained 
a  different  opinion.  He  finely  remarks :  "It  seems  impossible  to  see 
the  more  secret  and  noble  works  of  Nature  within  the  corpuscles,  by 
reason  of  their  transparency." — (Herschel,  On  Light,  Art.  1145.) 


240  FKAGMENTS  OF  SCIENCE. 

as  the  various  movements  of  the  earth's  surface  are  exe- 
cuted independently  of  the  orbital  revolution  of  our  planet. 

The  vapor  molecules  are  kept  asunder  by  forces  which, 
virtually  or  actually,  are  forces  of  repulsion.  Between 
these  elastic  forces  and  the  atmospheric  pressure  under 
which  the  vapor  exists,  equilibrium  is  established  as  soon 
as  the  proper  distances  between  the  molecules  have  been 
assumed.  If,  after  this,  the  molecules  be  urged  nearer  to 
each  'other  by  a  momentary  force,  they  recoil  as  soon  as 
the  force  is  expended.  If  they  be  separated  more  widely 
apart,  when  the  separating  force  ceases  to  act  they  again 
approach  each  other.  The  case  is  different  as  regards  the 
constituent  atoms. 

And  here  let  it  be  remarked,  that  we  are  now  upon  the 
very  outmost  verge  of  molecular  physics ;  and  that  I  am 
attempting  to  familiarize  your  minds  with  conceptions 
which  have  not  yet  obtained  universal  currency  even  among 
chemists ;  which  many  chemists,  moreover,  might  deem  un- 
tenable. But,  tenable  or  untenable,  it  is  of  the  highest  sci- 
entific importance  to  discuss  them.  Let  us,  then,  look  men- 
tally at  our  atoms  grouped  together  to  form  a  molecule. 
Every  atom  is  held  apart  from  its  neighbors  by  a  force  of 
repulsion ;  why,  then,  do  not  the  mutually  repellant  mem- 
bers of  this  group  part  company  ?  The  molecules  separate 
from  each  other  when  the  external  pressure  is  lessened  or 
removed,  but  the  atoms  do  not.  The  reason  of  this  stabil- 
ity is  that  two  forces,  the  one  attractive  and  the  other  re- 
pulsive, are  in  operation  between  every  two  atoms ;  and  the 
position  of  every  atom — its  distance  from  its  fellows — is 
determined  by  the  equilibration  of  these  two  forces.  If  the 
atoms  come  too  near,  repulsion  predominates  and  drives 
them  apart;  if  too  distant,  attraction  predominates  and 
draws  them  together.  The  point  at  which  attraction  and 
repulsion  are  equal  to  each  other  is  the  atom's  position  of 
equilibrium.  If  not  absolutely  cold — and  there  is  no  such 


CHEMICAL   RAYS.  241 

thing  as  absolute  coldness  in  our  corner  of  Nature — the 
atoms  are  always  in  a  state  of  vibration,  their  vibrations 
being  executed  to  and  fro  across  their  positions  of  equilib- 
rium. 

Into  a  vapor  thus  constituted,  we  have  now  to  pour  a 
beam  of  light ;  which  most  of  you  know  to  be  a  train  of 
minute  waves,  excited  in,  and  propagated  through,  an  al- 
most infinitely  attenuated  and  elastic  medium,  which  fills 
all  space,  and  which  we  name  the  ether.  It  is  hardly  neces- 
sary to  remind  you  that  these  waves  of  light  are  not  all  of 
the  same  size ;  that  some  of  them  are  much  longer  and 
higher  than  others  ;  that  the  short  waves  and  the  long  ones 
move  with  the  same  rapidity  through  space,  just  as  short 
and  long  waves  of  sound  travel  with  the  same  rapidity 
through  air,  and  that,  therefore,  the  shorter  waves  must  fol- 
low each  other  in  quicker  succession  than  the  longer  ones  ; 
that  the  different  rapidities  with  which  the  waves  of  light 
impinge  upon  the  retina,  or  optic  nerve,  give  rise  in  con- 
sciousness to  differences  of  color  /  that  there  are,  moreover, 
numberless  waves  emitted  by  the  sun  and  other  luminous 
bodies  which  reach  the  retina,  but  which  are  incompetent 
to  excite  the  sensation  of  light ;  for,  if  the  lengths  of  the 
waves  exceed  a  certain  limit,  or  if  they  fall  short  of  a  cer- 
tain other  limit,  they  cannot  generate  vision.  And  it  is  to 
be  particularly  borne  in  mind,  that  the  capacity  to  excite 
vision  does  not  depend  so  much  on  the  strength  of  the 
waves  as  on  their  periods  of  recurrence.  I  have,  as  many 
of  you  know,  permitted  waves  to  enter  my  own  eye,  which, 
if  their  energy  were  that  of  light,  would  have  instantly  and 
utterly  ruined  the  optic  nerve,  but  which  failed  to  produce 
any  impression  whatever  upon  consciousness,  because  their 
periods  were  not  those  competent  to  excite  the  retina. 

The  elements  of  all  the  conceptions  with  which  we  shall 
have  subsequently  to  deal  are  now  in  your  possession.  And 
you  will  observe  that,  though  we  are  speaking  of  things 
11 


242  FRAGMENTS  OF  SCIENCE. 

which  lie  entirely  beyond  the  range  of  the  senses,  the  con- 
ceptions are  as  truly  mechanical  as  they  would  be  if  w^e 
were  dealing  with  ordinary  masses  of  matter,  and  with 
wraves  of  sensible  magnitude.  No  really  scientific  mind  at 
the  present  day  will  be  disposed  to  draw  a  substantial  dis- 
tinction between  chemical  and  mechanical  phenomena. 
They  differ  from  each  other  as  regards  the  magnitude  of 
the  masses  involved  ;  but  in  this  sense  the  phenomena  of 
astronomy  differ,  also,  from  those  of  ordinary  mechanics. 
The  main  bent  of  the  natural  philosophy  of  a  future  age 
will  probably  be  to  chasten  into  order,  by  subjecting  it  to 
mechanical  laws,  the  existing  chaos  of  chemical  phe- 
nomena. 

Whether  we  see  rightly  or  wrongly — whether  our  in- 
tellection be  real  or  imaginary — it  is  of  the  utmost  im- 
portance in  science  to  aim  at  perfect  clearness  in  the  de- 
scription of  all  that  comes,  or  seems  to  come,  within  the 
range  of  the  intellect.  For,  if  we  are  right,  clearness  of 
utterance  forwards  the  cause  of  right ;  while,  if  we  are 
wrong,  it  insures  the  speedy  correction  of  error.  In  this 
spirit,  and  with  the  determination  at  all  events  to  speak 
plainly,  let  us  deal  with  our  conceptions  of  ether-waves  and 
molecules.  Supposing  a  wave,  or  a  train  of  waves,  to  im- 
pinge upon  a  molecule  so  as  to  urge  all  its  parts  with  the 
same  motion,  the  molecule  would  move  bodily  as  a  whole, 
but  because  they  are  animated  by  a  common  motion  there 
would  be  no  tendency  of  its  constituent  atoms  to  separate 
from  each  other.  Differential  motions  among  the  atoms 
themselves  would  be  necessary  to  effect  a  separation,  and 
if  such  motions  be  not  introduced  by  the  shock  of  the 
waves,  there  is  no  mechanical  ground  for  the  decomposition 
of  the  molecule. 

Thus  the  conception  of  the  decomposition  of  compound 
molecules  by  the  waves  of  ether  comes  to  us  recommended 
by  a  priori  probability.  But  a  closer  examination  of  the 


CHEMICAL  RAYS.  243 

question  compels  us  to  supplement,  if  not  materially  to 
qualify,  this  conception.  It  is  a  most  remarkable  fact  that 
the  waves  which  have  thus  far  been  found  most  effectual  in 
shaking-  asunder  the  atoms  of  compound  molecules  are 
those  of  least  mechanical  power.  Billows,  to  use  a  strong 
comparison,  are  incompetent  to  produce  effects  which  are 
readily  produced  by  ripples.  It  is,  for  example,  the  violet 
and  ultra-violet  rays  of  the  sun  that  are  most  effectual  in 
producing  these  chemical  decompositions ;  and,  compared 
with  the  red  and  ultra-red  solar  rays,  the  energy  of  these 
"  chemical  rays "  is  infinitesimal.  This  energy  would 
probably  in  some  cases  have  to  be  multiplied  by  millions 
to  bring  it  up  to  that  of  the  ultra-red  rays :  and  still  the 
latter  are  powerless  where  the  smaller  waves  are  potent. 
We  here  observe  a  remarkable  similarity  between  the  be- 
havior of  chemical  molecules  and  that  of  the  human  retina. 
The  energy  transmitted  to  the  eye  from  a  candle-flame  half 
a  mile  distant  is  more  than  sufficient  to  inform  conscious- 
ness ;  while  waves  of  a  different  period,  possessing  twenty 
thousand  million  times  this  energy,  have  been  suffered  to 
impinge  upon  my  own  retina,  with  an  absolute  unconscious- 
ness of  any  effect  whatever — mechanical,  physiological, 
chemical,  or  thermal. 

If,  then,  the  power  of  these  smaller  waves  to  unlock  the 
bonds  of  chemical  union  be  not  a  result  of  their  strength,  it 
must  be,  as  in  the  case  of  vision,  a  result  of  their  periods 
of  recurrence.  But  how  are  we  to  figure  this  action  ?  The 
shock  of  a  single  wave  produces  no  more  than  an  infini- 
tesimal effect  upon  an  atom  or  a  molecule.  To  produce  a 
larger  effect,  the  motion  must  accumulate,  and  for  wave- 
impulses  to  accumulate,  they  must  arrive  in  periods  iden- 
tical with  the  periods  of  vibration  of  the  atoms  on  which 
they  impinge.  In  this  case  each  successive  wave  finds  the 
atom  in  a  position  which  enables  that  wave  to  add  its  shock 
to  the  sum  of  the  shocks  of  its  predecessors.  The  effect  is 


244  FRAGMENTS  OF  SCIENCE. 

mechanically  the  same  as  that  due  to  the  timed  impulses 
of  a  boy  upon  a  swing.  The  single  tick  of  a  clock  has  no 
appreciable  effect  upon  the  unvibrating  and  equally  long 
pendulum  of  a  distant  clock ;  but  a  succession  of  ticks,  each 
of  which  adds,  at  the  proper  moment,  its  infinitesimal  push 
to  the  sum  of  the  pushes  preceding  it,  will,  as  a  matter  of 
fact,  set  the  second  clock  going.  So  likewise  a  single  puff 
of  air  against  the  prong  of  a  heavy  tuning-fork  produces 
no  sensible  motion,  and,  consequently,  no  audible  sound ; 
but  a  succession  of  puffs,  which  follow  each  other  in  periods 
identical  with  the  tuning-fork's  period  of  vibration,  will 
render  the  fork  sonorous.  I  think  the  chemical  action  of 
light  is  to  be  regarded  in  this  way.  Fact  and  reason  point 
to  the  conclusion  that  it  is  the  heaping  up  of  motion  on  the 
atoms,  in  consequence  of  their  synchronism  with  the  shorter 
waves,  that  causes  them  to  part  company.  This  I  take  to 
be  the  mechanical  cause  of  these  decompositions  which  are 
effected  by  the  waves  of  ether. 

And  now  let  us  return  to  that  faint  cloudiness  already 
mentioned,  from  which,  as  from  a  germ,  these  considerations 
and  speculations  have  sprung.  It  has  been  long  known  that 
light  effected  the  decomposition  of  a  certain  number  of 
bodies.  The  transparent  iodide  of  ethyl,  or  of  methyl,  for 
example,  becomes  brown  and  opaque  on  exposure  to  light, 
through  the  discharge  of  its  iodine.  The  art  of  photography 
is  founded  on  the  chemical  actions  of  light ;  so  that  it  is 
well  known  that  the  effects  for  which  the  foregoing  theoretic 
considerations  would  have  prepared  us,  are  not  only  proba- 
ble, but  actual. 

But  the  method  employed  in  the  experiments  in  which 
the  cloudiness  above  referred  to  was  observed,  and  which 
consists  simply  in  offering  the  vapors  of  volatile  substances 
to  the  action  of  light,  enables  us  not  only  to  give  such  ex- 
periments a  beautfiul  form,  but  also  to  give  a  great  exten- 
sion to  the  operations  of  light,  or  rather  of  radiant  force,  as 


CHEMICAL  RAYS. 


245 


a  chemical  agent.  It  also  enables  us  to  illustrate  in  our 
laboratories  actions  which  have  been  hitherto  performed 
only  in  the  laboratory  of  Nature.  A  few  of  these  actions 
of  a  representative  character  will  now  be  brought  before 
you;  and  advantage  will  be  taken  of  the  fact  that,  in  a 
great  number  of  cases,  one  or  more  of  the  substances  into 
which  the  waves  of  light  break  up  , 
compound  molecules  are  compar- 
atively involatile.  The  products 
of  decomposition  require  a  greater 
heat  than  is  required  by  the  va- 
pors from  which  they  are  derived 
to  keep  them  in  the  gaseous  form ; 
and  hence,  if  the  space  in  which 
these  new  bodies  are  liberated  be 
of  the  "proper  temperature,  they 
will  not  remain  in  the  vaporous 
condition,  but  will  precipitate 
themselves  as  liquid  particles,  thus 
forming  visible  clouds  upon  the 
beam,  to  the  action  of  which  they 
owe  their  existence. 

The  little  flask,  F,  in  the  an- 
nexed figure,  is  stopped  by  a  cork, 
pierced  in  two  places.  Through 
one  orifice  passes  a  narrow  glass 
tube,  #,  which  terminates  imme- 
diately under  the  cork;  through 
the  other  orifice  passes  a  similar 
tube,  #,  descending  to  the  bottom  of  the  little  flask,  which 
is  filled  to  a  height  of  about  an  inch  with  a  transparent 
liquid.  The  name  of  this  liquid  is  nitrite  of  amyl,  in  every 
molecule  of  which  we  have  5  atoms  of  carbon,  11  of  hydro- 
gen, 1  of  nitrogen,  and  2  of  oxygen.  Upon  this  group  the 
waves  of  our  electric  light  will  be  immediately  let  loose. 


246  FRAGMENTS  OF  SCIENCE. 

The  large  horizontal  tube  that  you  see  before  you  is  called 
an  "  experimental  tube ; "  it  is  connected  with  our  small 
flask ;  between  them,  however,  a  stop-cock  intervenes,  by 
means  of  which  the  passage  between  the  flask  and  the  ex- 
perimental tube  can  be  opened  or  closed  at  pleasure.  The 
other  tube,  passing  through  the  cork  of  the  flask  and  de- 
scending into  the  liquid,  is  connected  with  a  U-shaped  ves- 
sel, filled  with  fragments  of  clean  glass,  covered  with  sul- 
phuric acid.  In  front  of  the  U-shaped  vessel  is  a  narrow 
tube  stuffed  with  cotton-wool.  At  one  end  of  the  experi- 
mental tube  is  our  electric  lamp ;  and  here,  finally,  is  an  air- 
pump,  by  means  of  which  the  tube  has  been  exhausted. 
We  are  now  ready  for  experiment. 

Opening  the  cock  cautiously,  the  air  of  the  room  passes, 
in  the  first  place,  through  the  cotton-wool,  which  holds 
back  the  numberless  organic  germs  and  inorgani6  dust- 
particles  floating  in  the  atmosphere.  The  air,  thus  cleansed, 
passes  into  the  U-shaped  vessel,  where  it  is  dried  by  the 
sulphuric  acid.  It  then  descends  through  the  narrow  tube 
to  the  bottom  of  the  little  flask,  and  escapes  there  through 
a  small  orifice  into  the  liquid.  Through  this  it  bubbles, 
loading  itself  to  some  extent  with  the  nitrite-of-amyl  vapor, 
and  then  the  air  and  vapor  enter  the  experimental  tube 
together. 

The  closest  scrutiny  would  now  fail  to  discover  any 
thing  within  this  tube ;  it  is,  to  all  appearance,  absolutely 
empty.  The  air  and  the  vapor  are  both  invisible.  We 
will  permit  the  electric  beam  to  play  upon  this  mixture. 
The  lens  of  the  lamp  is  so  situated  as  to  render  the  beam 
slightly  convergent,  the  focus  being  formed  in  the  vapor 
at  about  the  middle  of  the  tube.  You  will  notice  that  the 
tube  remains  dark  for  a  moment  after  the  turning  on  of  the 
beam ;  but  the  chemical  action  will  be  so  rapid  that  atten- 
tion is  requisite  to  mark  this  interval  of  darkness.  I  ignite 
the  lamp ;  the  tube  for  a  moment  seems  empty ;  but  sud- 


CHEMICAL  RAYS.  247 

denly  the  beam  darts  through  a  luminous  white  cloud,  which 
has  banished  the  preceding  darkness.  It  has,  in  fact,  shaken 
asunder  the  molecules  of  the  nitrite  of  amyl,  and  brought 
down  upon  itself  a  shower  of  liquid  particles  which  causes 
it  to  flash  forth  in  your  presence  like  a  solid  luminous 
spear.  It  is  worth  while  to  mark  how  this  experiment 
illustrates  the  fact  that,  however  intense  a  luminous  beam 
may  be,  it  remains  invisible  unless  it  has  something  to 
shine  upon.  Space,  though  traversed  by  the  rays  from  all 
suns  and  all  stars,  is  itself  unseen.  Not  even  the  ether 
which  fills  space,  and  whose  motions  are  the  light  of  the 
universe,  is  itself  visible. 

You  notice  that  the  end  of  the  experimental  tube  most 
distant  from  the  lamp  is  free  from  cloud.  Now  the  nitrite- 
of-amyl  vapor  is  there  also,  but  it  is  unaffected  by  the 
powerful  beam  passing  through  it.  Let  us  make  the  trans- 
mitted beam  more  concentrated  by  receiving  it  on  a  con- 
cave silver  mirror,  and  causing  it  to  return  by  reflection  into 
the  tube.  It  is  still  powerless.  Though  a  cone  of  light  of 
extraordinary  intensity  now  traverses  the  vapor,  no  pre- 
cipitation occurs,  no  trace  of  cloud  is  formed.  Why  ?  Be- 
cause the  very  small  portion  of  the  beam  competent  to  de- 
compose the  vapor  is  quite  exhausted  by  its  work  in  the 
frontal  portions  of  the  tube.  The  great  body  of  the  light 
which  remains,  after  this  sifting  out  of  the  few  effectual 
rays,  has  no  power  over  the  molecules  of  nitrite  of  amyl. 
We  have  here,  strikingly  illustrated,  what  has  been  already 
stated  regarding  the  influence  of  period,  as  contrasted  with 
that  of  strength.  For  the  portion  of  the  beam  which  is  here 
ineffectual  has  probably  more  than  a  million  times  the  ab- 
solute energy  of  the  effectual  portion.  It  is  energy  specially 
related  to  the  atoms  that  we  here  need,  which  specially  re- 
lated energy  being  possessed  by  the  feeble  waves,  invests 
them  with  their  extraordinary  power.  When  the  experi- 
mental tube  is  reversed  so  as  to  bring  the  undecomposed 


248  FRAGMENTS  OF  SCIENCE. 

vapors  under  the  action  of  the  unsifted  beam,  you  have  in- 
stantly this  fine  luminous  cloud  precipitated. 

The  light  of  the  sun  also  effects  the  decomposition  of 
the  uitrite-of-amyl  vapor.  A  small  room  in  the  Royal 
Institution,  into  which  the  sun  shone,  was  partially  dark- 
ened, the  light  being  permitted  to  enter  through  an  open 
portion  of  the  window-shutter.  In  the  track  of  the  beam 
was  placed  a  large  plano-convex  lens,  which  formed  a  fine 
convergent  cone  in  the  dust  of  the  room  behind  it.  The 
experimental  tube  was  filled  in  the  laboratory,  covered 
with  a  black  cloth,  and  carried  into  the  partially-dark- 
ened room.  On  thrusting  one  end  of  the  tube  into  the 
cone  of  rays  behind  the  lens,  precipitation  within  the  cone 
was  copious  and  immediate.  The  vapor  at  the  distant  end 
of  the  tube  was  shielded  by  that  in  front ;  but  on  revers- 
ing the  tube,  a  second  and  similar  splendid  cone  was  pre- 
cipitated. 

Now  let  us  pause  for  a  moment  and  glance  at  the 
ground  over  which  we  have  passed.  We  have  defined  a 
vapor  as  an  aggregate  of.  molecules  mutually  repellent, 
but  hindered  from  indefinitely  retreating  from  each  other 
by  an  external  pressure.  We  have  defined  a  molecule  as 
an  aggregate  of  atoms  maintained  in  positions  of  equi- 
librium by  the  equalized  action  of  two  opposing  forces, 
and  always  oscillating  to  and  fro  across  those  positions. 
We  have  defined  a  beam  of  light  as  a  train  of  innumerable 
waves,  and  have  illustrated  then*  chemical  action.  We 
have  learned  that  it  is  not  the  magnitude  or  power  of  the 
waves,  so  much  as  their  periods  of  recurrence,  that  renders 
them  effectual  as  chemical  agents.  We  have  also  seen 
how  the  luminous  beam  is  sifted  by  the  vapor  which  it 
decomposes,  and  deprived  of  those  rays  which  are  com- 
petent to  effect  the  decomposition.  The  effects,  moreover, 
obtained  with  the  electric  beam  are  also  produced  by  the 
beams  of  the  sun. 


CHEMICAL  RAYS.  249 

And  here  I  would  ask  you  to  make  familiar  to  your 
minds  the  idea  that  no  chemical  action  can  be  produced  by 
a  ray  that  does  not  involve  the  destruction  of  the  ray.  But 
the  term  "  ray "  is  unsatisfactory  to  us  at  present,  when 
our  desire  is  to  abolish  all  vagueness,  and  to  affix  a  definite 
physical  significance  to  each  of  our  terms.  Abandoning 
the  term  ray  as  loose  and  indefinite,  we  have  to  fix  our 
thoughts  upon  the  waves  of  light ;  and  to  render  clear  to 
our  minds  that  those  waves  which  produce  chemical  action 
do  so  by  delivering  up  their  own  motion  to  the  molecules 
which  they  decompose.  We  have  here  forestalled  to  some 
extent  a  question  of  great  importance  in  molecular  physics, 
which,  however,  is  worthy  of  being  fixed  more  definitely  in 
your  mind ;  it  is  this :  When  the  waves  of  ether  are  in- 
tercepted by  a  compound  vapor,  is  the  motion  of  the  waves 
transferred  to  the  molecules  of  the  vapor,  or  to  the  atoms 
of  the  molecules  ?  We  have  thus  far  leaned  to  the  con- 
clusion that  the  motion  is  communicated  to  the  atoms ;  for 
if  not  to  these  individually,  why  should  they  be  shaken 
asunder  ?  The  question,  however,  is  capable  of,  and  is 
worthy  of,  another  test,  the  bearing  and  significance  of 
which  you  will  immediately  appreciate. 

As  already  explained,  the  molecules  are  held  in  their 
positions  of  equilibrium  by  their  mutual  repulsion  on  the 
one  side,  and  by  an  external  pressure  on  the  other.  Their 
rate  of  vibration,  if  they  vibrate  at  all,  must  depend  upon 
the  elastic  force  which  they  mutually  exert.  If  this  force 
be  changed,  the  rate  of  vibration  must  change  along  with 
it;  and  after  the  change  the  molecules  could  no  longer 
absorb  the  waves  which  they  absorbed  prior  to  the  change. 
Now,  the  elastic  force  between  molecule  and  molecule  is 
utterly  altered  when  a  vapor  passes  to  the  liquid  state. 
Hence,  if  the  liquid  absorbs  waves  of  the  same  period  as  its 
vapor,  it  is  a  proof  that  the  absorption  is  not  effected  by 
the  molecules.  Let  us  be  perfectly  clear  on  this  important 


250  FRAGMENTS  OF  SCIENCE. 

point.  Those  waves  are  absorbed  whose  vibrations  syn- 
chronize with  those  of  the  molecules  or  atoms  on  which 
they  impinge ;  a  principle  which  is  sometimes  expressed  by 
saying  that  bodies  radiate  and  absorb  the  same  rays.  This 
great  law,  as  you  know,  is  the  foundation  of  spectrum- 
analysis  ;  it  enabled  Kirchhoff  to  explain  the  lines  of  Frauen- 
hofer,  and  to  determine  the  chemical  composition  of  the 
atmosphere  of  the  sun.  If,  then,  after  such  a  change  as 
that  involved  in  the  passage  of  a  vapor  to  the  liquid  state, 
the  same  waves  are  absorbed  as  were  absorbed  prior  to  the 
passage,  it  is  a  proof  that  the  molecules,  which  must  have 
utterly  changed  their  periods,  cannot  be  the  seat  of  the  ab- 
sorption ;  and  we  are  driven  to  conclude  that  it  is  to  the 
atoms,  whose  rates  of  vibration  are  unchanged  by  the 
change  of  aggregation,  that  the  wave-motion  is  transferred. 
If  experiment  should  prove  this  identity  of  action  on  the 
part  of  a  vapor  and  its  liquid,  it  would  establish  in  a  new 
and  striking  manner  the  conclusion  to  which  we  have  pre- 
viously leaned. 

We  will  now  resort  to  the  experimental  test.  In  front 
of  this  experimental  tube,  which  contains  a  quantity  of  the 
nitrite-of-amyl  vapor,  is  placed  a  glass  cell  a  quarter  of  an 
inch  in  thickness,  filled  with  the  liquid  nitrite  of  amyl.  I 
send  the  electric  beam  first  through  the  liquid  and  then 
through  its  vapor.  The  luminous  power  of  this  beam  is 
very  great,  but  it  can  make  no  impression  upon  the  vapor. 
The  liquid  has  robbed  it  completely  of  its  effective  waves. 
When  the  liquid  is  removed  chemical  action  immediately 
commences,  and  in  a  moment  we  have  the  apparently 
empty  tube  filled  with  this  bright  cloud,  precipitated  by 
one  portion  of  the  beam,  and  illuminated  by  another.  Thus 
we  uncover  to  some  extent  the  secrets  of  this  world  of 
molecules  and  atoms. 

Instead  of  employing  air  as  the  vehicle  by  which  the 
vapor  is  carried  into  the  experimental  tube,  we  may  em- 


CHEMICAL  RAYS.  251 

ploy  oxygen,  hydrogen,  or  nitrogen.  With  hydrogen  curi- 
ous effects  are  observed,  due  to  the  sinking  of  the  clouds 
through  the  extremely  light  gas  in  which  they  float.  They 
illustrate,  but  do  not  prove,  the  untenable  notion  of  those 
who  say  that  the  clouds  of  our  own  atmosphere  could  not 
float  if  the  cloud-particles  were  not  little  bladders  instead 
of  full  spheres.  Before  you  is  a  tube  filled  with  the  nitrite- 
of-amyl  vapor,  which  has  been  carried  into  the  tube  by 
hydrogen  gas.  On  sending  the  beam  through  the  tube  a 
delicate  bluish-white  cloud  is  precipitated.  A  few  strokes 
of  the  pump  clear  the  tube  of  this  cloud,  but  leave  a  resi- 
due of  vapor  behind.  Again,  turning  on  the  beam  we  have 
a  second  cloud,  more  delicate  than  the  first.  This  may  be 
done  half  a  dozen  times  in  succession.  A  residue  of  vapor 
will  still  linger  in  the  tube  sufficient  to  yield  a  cloud  of  ex- 
quisite delicacy,  both  as  regards  color  and  texture. 

Besides  the  nitrite  of  amyl,  a  great  number  of  other 
substances  might  be  employed,  which,  like  the  nitrite,  have 
been  hitherto  not  known  to  be  chemically  susceptible  to 
light.  This  is,  in  fact,  a  representative  case.  One  point 
in  addition  I  wish  to  illustrate,  chiefly  because  the  effect  is 
the  same  in  kind  as  one  of  great  importance  in  nature.  Our 
atmosphere  contains  carbonic-acid  gas,  which  furnishes  food 
to  the  vegetable  world.  But  this  food,  as  many  of  you 
know,  could  not  be  consumed  by  plants  and  vegetables 
without  the  intervention  of  the  sun's  rays.  As  far  as  we 
know,  however,  these  rays  are  powerless  upon  the  free  car- 
bonic acid  of  our  atmosphere ;  the  sun  can  only  decompose 
the  gas  when  it  is  absorbed  by  the  leaves  of  plants.  In  the 
leaves  the  carbonic  acid  is  in  close  proximity  with  sub- 
stances ready  to  take  advantage  of  the  loosening  of  the 
molecules  by  the  waves  of  light.  Incipient  disunion  being 
introduced  by  the  solar  rays,  the  carbon  of  the  gas  is  seized 
upon  by  the  leaf  and  appropriated,  while  the  oxygen  is  dis- 
charged into  the  atmosphere. 


252  FRAGMENTS  OF  SCIENCE. 

The  experimental  tube  now  before  you  contains  a 
quantity  of  a  different  vapor  from  that  which  we  have 
hitherto  employed.  The  liquid  from  which  this  vapor  is 
derived  is  called  the  nitrite  of  butyl.  On  sending  the  elec- 
tric beam  through  the  vapor,  which  has  been  carried  in  by 
air,  the  chemical  action  is  insensible.  I  add  to  the  vapor  a 
quantity  of  air  which  has  been  permitted  to  bubble  through 
hydrochloric  acid.  When  the  beam  is  now  turned  on,  so 
rapid  is  the  action  and  so  dense  the  clouds  precipitated, 
that  you  could  hardly,  by  an  effort  of  attention,  observe  the 
dark  interval  which  preceded  the  precipitation  of  the  cloud. 
This  enormous  augmentation  of  the  action  is  due  to  the 
presence  of  the  hydrochloric  acid.  Like  the  chlorophyl  in 
the  leaves  of  plants,  it  takes  advantage  of  the  loosening  of 
the  molecules  of  nitrite  of  butyl  by  the  waves  of  the  electric 
light. 

In  these  experiments  we  have  employed  a  luminous 
beam  for  two  different  purposes.  A  small  portion  of  it  has 
been  devoted  to  the  decomposition  of  our  vapors,  while  the 
great  body  of  the  light  has  served  to  render  luminous  the 
clouds  resulting  from  the  decomposition.  It  is  possible  to 
impart  to  these  clouds  any  required  degree  of  tenuity,  for 
it  is  in  our  power  to  limit  at  pleasure  the  amount  of  vapor 
in  our  experimental  tube.  When  the  quantity  is  duly 
limited,  the  precipitated  particles  are  at  first  inconceivably 
small,  defying  the  highest  microscopic  power  to  bring  them 
within  the  range  of  vision.  Probably  their,  diameters  might 
then  be  expressed  in  millionths  of  an  inch.  They  grow 
gradually,  and  as  they  augment  in  size  they  scatter  a  con- 
tinually increasing  quantity  of  wave-motion,  until  finally 
the  cloud  which  they  form  becomes  so  luminous  as  to  fill 
this  theatre  with  light.  During  the  growth  of  the  particles 
the  most  splendid  iridescences  are  often  exhibited.  Such 
I  have  sometimes  seen  with  delight  and  wonder  in  the 
atmosphere  of  the  Alps,  but  never  any  thing  so  gorgeous 


STRUCTURE  AND  LIGHT  OF  THE  SKY.  253 

as  those  which  our  laboratory  experiments  reveal.  It  is 
not,  however,  with  the  iridescences,  however  beautiful  they 
may  be,  that  we  have  now  to  occupy  our  thoughts,  but 
with  other  effects  which  bear  upon  the  two  great  standing 
enigmas  of  meteorology — the  color  of  the  sky  and  the  polar- 
ization of  its  light. 

It  is  possible,  as  stated,  by  duly  regulating  the  quantity 
of  vapor,  to  make  our  precipitated  particles  grow  from  an 
infinitesimal  and  altogether  ultra-microscopic  size  to  masses 
of  sensible  magnitude  ;  and  by  means  of  these  particles,  in 
a  certain  stage  of  their  growth,  we  can  produce  a  blue 
which  shall  rival,  if  it  does  not  transcend,  that  of  the  deepest 
and  purest  Italian  sky.  Let  this  point  be  in  the  first  place 
established.  Associated  with  our  experimental  tube  is  a 
barometer,  the  mercurial  column  of  which  now  indicates 
that  the  tube  is  exhausted.  Into  the  tube  is  introduced  a 
quantity  of  the  mixed  air  and  nitrite-of-butyl  vapor  sufficient 
to  depress  the  mercurial  column  one-twentieth  of  an  inch ; 
that  is  to  say,  the  air  and  vapor  together  exert  a  pressure 
of  one  six-hundredth  of  an  atmosphere.  I  now  add  a  quan- 
tity of  air  and  hydrochloric  acid  sufficient  to  depress  the 
mercury  half  an  inch  farther,  and  into  this  compound  and 
highly-attenuated  atmosphere  I  discharge  the  beam  of  the 
electric  light.  The  effect  is  slow ;  but  gradually  within  the 
tube  arises  this  splendid  azure,  which  strengthens  for  a  time, 
reaches  a  maximum  of  depth  and  purity,  and  then,  as  the 
particles  grow  larger,  passes  into  whitish  blue.  This. ex- 
periment is  representative,  and  it  illustrates  a  general 
principle.  Various  other  colorless  substances  of  the  most 
diverse  properties,  optical  and  chemical,  might  be  employed 
for  this  experiment.  The  incipient  cloud  in  every  case 
would  exhibit  this  superb  blue  ;  thus  proving  to  demonstra- 
tion that  particles  of  infinitesimal  size,  without  any  color  of 
their  own,  and  irrespective  of  those  optical  properties  ex- 
hibited by  the  substance  in  a  massive  state,  are  competent 
to  produce  the  color  of  the  sky. 


254  FRAGMENTS  OF  SCIENCE. 

But  there  is  another  subject  connected  with  our  firma- 
ment, of  a  more  subtle  and  recondite  character  than  even 
its  color.  I  mean  that  "  mysterious  and  beautiful  phenom- 
enon," '  the  polarization  of  the  light  of  the  sky.  The  po- 
larity of  a  magnet  consists  in  its  two-endedness,  both  ends, 
or  poles,  acting  in  opposite  ways.  Polar  forces,  as  most  of 
you  know,  are  those  in  which  the  duality  of  attraction  and 
repulsion  is  manifested.  And  a  kind  of  two-sidedness — 
noticed  by  Huyghens,  commented  on  by  Newton,  and  dis- 
covered by  a  French  philosopher,  named  Malus,  in  a  beam 
of  light  which  had  been  reflected  from  one  of  the  windows 
of  the  Luxembourg  Palace  in  Paris — receives  the  name  of 
polarization.  "We  must  now,  however,  attach  a  distinct- 
ness to  the  idea  of  a  polarized  beam,  which  its  discoverers 
were  not  able  to  attach  to  it.  For  in  their  day  men's 
thoughts  were  not  sufficiently  ripe,  nor  optical  theory  suffi- 
ciently advanced,  to  seize  upon  or  express  the  physical 
meaning  of  polarization.  When  a  gun  is  fired,  the  explo- 
sion is  propagated  as  a  wave  through  the  air.  The  shells 
of  air,  if  I  may  use  the  term,  surrounding  the  centre  of  con- 
cussion, are  successively  thrown  into  motion,  each  shell 
yielding  up  its  motion  to  that  in  advance  of  it,  and  return- 
ing to  its  position  of  equilibrium.  Thus,  while  the  wave 
travels  through  long  distances,  each  individual  particle  of 
air  concerned  in  its  transmission  performs  merely  a  small 
excursion  to  and  fro.2  In  the  case  of  sound,  the  vibrations 
of  the  air-particles  are  executed  in  the  direction  in  which 
the  sound  travels.  They  are,  therefore,  called  longitudinal 
vibrations.  In  the  case  of  light,  on  the  contrary,  the  vibra- 
tions are  transversal;  that  is  to  say,  the  individual  particles 
of  ether  move  to  and  fro  across  the  direction  in  which  the 
light  is  propagated.  In  this  respect  waves  of  light  resem- 
ble ordinary  water-waves,  more  than  waves  of  sound.  In 

1  Herschel's  Meteorology,  Art.  233. 

2  Lectures  on  Sound,  p.  3.     (Longmans.) 


STRUCTURE  AND   LIGHT   OF  THE  SKY.  255 

the  case  of  an  ordinary  beam  of  light,  the  vibrations  of  the 
ether-particles  are  executed  in  every  direction  perpendicular 
to  it ;  but  let  the  beam  impinge  obliquely  upon  a  plane- 
glass  surface,  as  in  the  case  of  Malus,  the  portion  reflected 
will  no  longer  have  its  particles  vibrating  in  all  directions 
round  it.  By  the  act  of  reflection,  if  it  occur  at  the  proper 
angle,  the  vibrations  are  all  confined  to  a  single  plane,  and 
light  thus  circumstanced  is  called  plane  polarized  light. 

A  beam  of  light  passing  through  ordinary  glass  executes 
its  vibrations  within  the  substance  exactly  as  it  would  do 
in  air,  or  in  ether-filled  space.  Not  so  when  it  passes 
through  many  transparent  crystals.  For  these  have  also 
their  two-sidedness,  the  arrangement  of  their  molecules 
being  such  as  to  tolerate  vibrations  only  in  certain  definite 
directions.  There  is  the  well-known  crystal  tourmaline, 
which  shows  a  marked  hostility  to  all  vibrations  executed 
at  right  angles  to  the  axis  of  the  crystal.  It  speedily  ex- 
tinguishes such  vibrations,  while  those  executed  parallel  to 
the  axis  are  freely  propagated.  The  consequence  is,  that  a 
beam  of  light,  after  it  has  passed  through  any  thickness  of 
this  crystal,  emerges  from  it  polarized.  So  also  as  regards 
the  beautiful  crystal  known  as  Iceland  spar,  or  as  double- 
refracting  spar.  In  one  direction,  but  in  one  only,  it  acts 
like  a  piece  of  glass ;  in  all  other  directions  it  splits  the 
beam  of  light  passing  through  it  into  two  distinct  halves, 
both  of  which  are  perfectly  polarized,  their  vibrations  being 
executed  in  two  planes,  at  right  angles  to  each  other. 

It  is  possible  by  a  suitable  contrivance  to  get  rid  of  one 
of  the  two  polarized  beams  into  which  Iceland  spar  divides 
an  ordinary  beam  of  light.  This  was  done  so  ingeniously 
and  effectively  by  a  man  named  Nicol,  that  the  Iceland  spar, 
cut  in  his  fashion,  is  now  universally  known  as  Nicol's  prism. 
Such  a  prism  can  polarize  a  beam  of  light,  and  if  the  beam, 
before  it  impinges  on  the  prism,  be  already  polarized,  in 
one  position  of  the  prism  it  is  stopped,  while  in  another 


256  FRAGMENTS  OF  SCIENCE. 

position  it  is  transmitted.  Our  way  is  now,  to  some  extent, 
cleared  toward  an  examination  of  the  light  of  the  sky. 
Looking  at  various  points  of  the  blue  firmament  through  a 
Nicol's  prism,  and  turning  the  prism  round  its  axis,  we  im- 
mediately notice  variations  of  brightness.  In  certain  posi- 
tions of  the  prism,  and  from  certain  points  of  the  firmament, 
the  light  appears  to  be  freely  transmitted ;  while  it  is  only 
necessary  to  turn  the  prism  round  its  axis  through  an  angle 
of  90°  to  materially  diminish  the  intensity  of  the  light.  On 
close  scrutiny  it  is  found  that  the  difference  produced  by 
the  rotation  of  the  prism  is  greatest  when  the  sky  is  re- 
garded in  a  direction  at  right  angles  to  that  of  the  solar 
rays  through  the  air. 

Let  me  describe  a  few  actual  observations  made  some 
days  ago  on  Primrose  Hill.  The  sun  was  near  setting,  and 
a  few  scattered  neutral-tint  clouds,  which  failed  to  catch 
the  dying  light,  were  floating  in  the  air.  When  these  were 
looked  at  across  the  track  of  the  solar  beams,  it  was  pos- 
sible, by  turning  the  Nicol  round,  to  see  them  either  as 
white  clouds  on  a  dark  ground,  or  as  dark  clouds  on  a  bright 
ground.1  In  certain  positions  of  the  prisms  the  sky-light 
was  in  great  part  quenched,  and  then  the  clouds,  projected 
against  the  darkness  of  space,  appeared  white.  Turning 
the  Nicol  90°  round  its  axis,  the  brightness  of  the  sky  was 
restored,  the  clouds  becoming  dark  through  contrast  with 
this  brightness.  Experiments  of  this  kind  prove  that  the 
blue  light  sent  to  us  by  the  firmament  is  polarized,  and  that 
the  direction  of  most  perfect  polarization  is  perpendicular 
to  the  solar  rays.  Were  the  heavenly  azure  like  the  light 
scattered  from  a  thick  cloud,  the  turning  of  the  prism  would 
have  no  effect  upon  it ;  it  would  be  transmitted  equally  dur- 
ing the  entire  rotation  of  the  prism.  The  light  of  the  sky  is 
in  great  part  quenched,  because  it  is  in  great  part  polarized. 

1 1  was  not  aware  when  these  words  were  written  that  this  observation 
was  made  by  the  indefatigable  Brewster. 


STRUCTURE  AND   LIGHT  OF  THE  SKY.  257 

When  a  luminous  beam  impinges  at  the  proper  angle 
on  a  plane-glass  surface  it  is  polarized  by  reflection.  It  is 
polarized,  in  part,  by  all  oblique  reflections ;  but  at  one 
particular  angle,  the  reflected  light  is  perfectly  polarized. 
An  exceedingly  beautiful  and  simple  law,  discovered  by 
Sir  David  Brewster,  enables  us  readily  to  find  the  polarizing 
angle  of  any  substance  whose  refractive  index  is  known. 
This  law  was  discovered  experimentally  by  Brewster ;  but 
the  "Wave  Theory  of  light  renders  a  complete  reason  for 
the  law.  A  geometrical  image  of  it  is  thus  given  :  When 
a  beam  of  light  impinges  obliquely  upon  a  plate  of  glass  it 
is  in  part  reflected  and  in  part  refracted.  At  one  particular 
incidence  the  reflected  and  the  refracted  portions  of  the 
beam  are  at  right  angles  to  each  other.  The  angle  of  inci- 
dence is  then  the  polarizing  angle.  It  varies  with  the  re- 
fractive index  of  the  substance ;  being  for  water  52^,  for 
glass  57£,  and  for  diamond  68°. 

It  has  been  already  stated  that,  in  order  to  obtain  the 
most  perfect  polarization  of  the  firmamental  light,  the  sky 
must  be  regarded  in  a  direction  at  right  angles  to  the  solar 
beams.  This  is  sometimes  expressed  by  saying  that  the 
place  of  maximum  polarization  is  at  an  angular  distance  of 
90°  from  the  sun.  This  angle,  enclosed  as  it  is  between  the 
direct  and  reflected  rays,  comprises  both  the  angles  of  inci- 
dence and  reflection,  supposing  the  polarization  to  be  due 
to  a  single  reflection.  Hence  the  angle  of  incidence  is  half 
of  90°,  or  45°.  This  is  the  atmospheric  polarizing  angle, 
and  the  question  is,  what  known  substance  possesses  an 
index  of  refraction  to  correspond  with  this  polarizing  angle  ? 
"  If,"  says  Sir  John  Herschel,  "  we  knew  this  substance,  we 
might  be  tempted  to  conclude  that  particles  of  it,  scattered 
in  the  atmosphere,  produce  the  polarization  of  the  sky. 
Were  the  angle  of  maximum  polarization  76°  (instead  of 
90°),  we  should  look  to  water  or  ice,  as  the  reflecting  body, 
however  inconceivable  the  existence  in  a  cloudless  atmos- 


258  FRAGMENTS  OF  SCIENCE. 

phere  and  a  hot  summer  day,  of  unevaporated  particles  of 
water."  But  a  polarizing  angle  of  45°  corresponds  to  a 
refractive  index  of  1 ;  this  means  that  there  is  no  refraction 
at  all,  in  which  case  we  ought  to  have  no  reflection.  Brew- 
ster,  therefore,  and  others  came  to  the  conclusion  that  the 
reflection  was  from  the  particles  of  air  themselves.  Dr. 
Rubenson,  of  Upsala,  made  the  angle  enclosed  between  the 
direct  and  reflected  beams  90°  2' ;  "  the  half  of  which,"  says 
Mr.  Buchan,  in  his  excellent  little  "Handy  Book  of  Me- 
teorology," "  is  so  near  the  polarizing  angle  of  air  as  to  leave 
no  doubt  that  the  light  of  the  sky,  as  first  stated  by  Brew- 
ster,  is  polarized  by  reflection  from  the  particles  of  air." 

If  you  doubt  the  wisdom,  acknowledge,  at  all  events, 
the  faith  in  your  capacity  which  has  caused  me  to  bring 
so  entangled  a  subject  before  you.  I  would  fain  believe, 
however,  that  even  the  intellect  which  draws  its  culture 
from  a  totally  different  source,  may  have  its  interest  excited 
in  subjects  like  the  present,  dark  and  difficult  though  they 
seem.  I  do  not  expect  that  you  will  grasp  all  the  details 
of  this  discussion  ;  but  everybody  present  will,  I  think,  see 
the  extremely  important  part  hitherto  played  by  the  law 
of  Brewster  in  speculations  as  to  the  color  and  polarization 
of  the  sky.  Let  me  now  endeavor  to  demonstrate  in  your 
presence,  firstly,  and  in  confirmation  of  our  former  experi- 
ments, that  sky-blue  may  be  produced  by  exceedingly  mi- 
nute particles  of  any  kind  of  matter  ;  secondly,  that  polari- 
zation identical  with  that  of  the  sky  is  produced  by  such 
particles ;  and  thirdly,  that  matter  in  this  fine  state  of  di- 
vision, where  its  particles  are  small  in  comparison  with  the 
height  and  span  of  a  wave  of  light,  releases  itself  completely 
from  the  law  of  Brewster  ;  the  direction  of  maximum  polari- 
zation being  absolutely  independent  of  the  polarizing  angle 
as  hitherto  defined. 

Into  this  experimental  tube,  in  the  manner  already  de- 
scribed, I  introduce  a  vapor  which  is  decomposable  by  the 


STRUCTURE-  AND   LIGHT  OF  THE   SKY.  259 

waves  of  light.  The  mixed  air  and  vapor  are  sufficient  to 
depress  the  mercurial  column  one  inch.  I  add  to  this  mix- 
ture air,  which  has  been  permitted  to  bubble  through  dilute 
hydrochloric  acid,  until  the  column  is  depressed  thirty  inches : 
in  other  words,  until  the  tube  is  full.  And  now  I  permit 
the  electric  beam  to  play  upon  the  mixture.  For  some 
time  nothing  is  seen.  The  chemical  action  is  doubtless 
progressing,  and  condensation  is  going  on ;  but  the  con- 
densing molecules  have  not  yet  coalesced  to  particles  suffi- 
ciently large  to  reflect  sensibly  the  waves  of  light.  As 
before  stated — and  the  statement  rests  upon  an  experimental 
basis — the  particles  here  generated  are  at  first  so  small  that 
their  diameters  would  probably  have  to  be  expressed  in 
millionths  of  an  inch  ;  while  to  form  each  of  these  particles 
whole  crowds  of  molecules  are  probably  aggregated.  Helped 
by  such  considerations  the  intellectual  vision  plunges  more 
profoundly  into  atomic  Nature,  and  shows  us,  among  other 
things,  how  far  we  are  from  the  realization  of  Newton's 
hope  that  the  molecules  might  one  day  be  seen  by  micro- 
scopes. While  I  am  speaking,  you  observe  this  delicate  blue 
color,  forming  and  strengthening  within  the  experimental 
tube.  No  sky-blue  could  exceed  it  in  richness  and  purity  ; 
but  the  particles  which  produce  this  color  lie  wholly  beyond 
our  microscopic  range.  A  uniform  color  is  here  developed, 
which  has  as  little  breach  of  continuity — which  yields  as 
little  evidence  of  the  particles  concerned  in  its  production, 
as  that  yielded  by  a  body  whose  color  is  due  to  true  mo- 
lecular absorption.  This  blue  is  at  first  as  deep  and  dark 
as  the  sky  seen  from  the  highest  Alpine  peaks,  and  for  the 
same  reason.  But  it  grows  gradually  brighter,  still  main- 
taining its  blueness,  until  at  length  a  whitish  tinge  mingles 
with  the  pure  azure  ;  announcing  that  the  particles  are  now 
no  longer  of  that  infinitesimal  size  which  mainly  scatters 
the  shortest  waves.1 

1  Possibly  a  photographic  impression  might  be  taken  long  before  the 
blue  becomes  visible,  for  the  ultra-blue  rays  are  first  reflected. 


260  FRAGMENTS  OF  SCIENCE. 

The  liquid  here  employed  is  the  iodide  of  allyl,  but  I 
might  choose  any  one  of  a  dozen  substances  here  before 
me  to  produce  the  effect.  You  have  seen  what  may  be 
done  with  the  nitrite  of  butyl.  With  nitrite  of  amyl,  bisul- 
phide of  carbon,  benzol,  benzoic  ether,  etc.,  the  same  blue 
color  may  be  produced.  In  all  cases,  where  matter  slowly 
passes  from  the  molecular  to  the  massive  state  the  transi- 
tion is  marked  by  the  production  of  the  blue.  More  than 
this  :  you  have  seen  me  looking  at  the  blue  color  (I  hardly 
like  to  call  it  a  blue  "  cloud,"  its  texture  and  properties  are 
so  different  from  ordinary  clouds)  through  this  bit  of  spar. 
This  is  a  Nicol's  prism,  and  it  is  to  be  wished  that  one  of 
them  could  be  placed  in  the  hands  of  each  of  you.  Now, 
this  blue  that  I  have  been  regarding  turns  out  to  be,  if  the 
expression  be  allowed,  a  bit  of  more  perfect  sky  than  the 
sky  itself.  On  looking  across  the  illuminating  beam  as  we 
look  across  the  solar  rays  in  the  atmosphere,  we  obtain  not 
only  partial  polarization,  but  perfect  polarization.  In  one 
position  of  the  Nicol  the  blue  light  passes  freely  to  the  eye ; 
in  the  other  it  is  absolutely  cut  off,  the  experimental  tube 
being  reduced  to  optical  emptiness.  It  is  well  to  place  a 
black  surface  behind  the  experimental  tube,  so  as  to  prevent 
foreign  light  from  troubling  the  eye.  In  one  position  of 
the  prism  this  black  surface  is  seen  without  softening  or 
qualification;  for  the  particles  within  the  tube  are  them- 
selves invisible,  and  the  light  which  they  scatter  is  quenched. 
If  the  light  of  the  sky  were  polarized  with  the  same  per- 
fection, on  looking  properly  toward  it  through  a  Nicol  we 
should  meet,  not  the  mild  radiance  of  the  firmament,  but 
the  unillumined  blackness  of  space. 

The  construction  of  a  Nicol's  prism  is  such  that  it 
allows  the  passage  of  vibrations  which  are  executed  in  a 
certain  determinate  direction,  and  these  only.  All  vibra- 
tions executed  at  right  angles  to  this  direction  are  com- 
pletely stopped :  while  components  only  of  those  executed 


STRUCTURE  AND   LIGHT   OF   THE   SKY.  261 

obliquely  to  it  are  transmitted.  It  is  easy,  therefore,  to  see 
that,  from  the  position  in  which  the  prism  must  be  held  to 
transmit  or  to  quench  the  light  of  our  incipient  cloud,  we 
can  infer  the  direction  of  the  vibrations  of  that  light.  You 
will  be  able  to  picture  those  vibrations  without  difficulty. 
Suppose  a  line  drawn  from  any  point  of  the  "  cloud  "  per- 
pendicular to  the  illuminating  beam.  The  particles  of  ether 
along  that  line,  which  carry  the  light  from  the  cloud  to  the 
eye,  vibrate  in  a  direction  perpendicular  both  to  the  line 
and  to  the  beam.  And  if  any  number  of  lines  be  drawn 
in  the  same  way  from  the  cloud,  like  the  spokes  of  a  wheel, 
the  particles  of  ether  along  all  of  them  oscillate  in  the  same 
manner.  Wherefore,  if  a  plane  surface  be  imagined  cutting 
the  incipient  cloud  at  rigbt  angles  to  its  length,  the  vibra- 
tions discharged  laterally  are  all  parallel  to  this  surface. 
This  is  the  plane  of  vibration  of  the  polarized  light. 

Our  incipient  blue  cloud  is  a  virtual  Nicol's  prism,  and, 
between  it  and  the  real  prism,  we  can  produce  all  the 
effects  obtainable  between  the  polarizer  and  analyzer  of  a 
polariscope.  When,  for  example,  a  thin  plate  of  selenite, 
which  is  crystallized  sulphate  of  lime,  is  placed  between 
the  Nicol  and  the  incipient  cloud,  we  obtain  the  splendid 
chromatic  phenomena  of  polarized  light.  The  color  of  the 
gypsum-plate,  as  many  of  you  know,  depends  upon  its 
thickness.  If  this  be  uniform,  the  color  is  uniform.  If,  on 
the  contrary,  the  plate  be  wedge-shaped,  thickening  grad- 
ually and  uniformly  from  edge  to  back,  we  have  brilliant 
bands  of  color  produced  parallel  to  the  edge  of  the  wedge. 
Perhaps  the  best  form  of  plate  for  experiments  of  this 
character  is  that  now  in  my  hand,  which  was  prepared  for 
me  some  years  ago  by  a  man  of  genius  in  his  way,  the  late 
Mr.  Darker,  of  Lambeth.  It  consists  of  a  plate  of  selenite 
thin  at  the  centre,  and  gradually  thickening  toward  the 
circumference.  Placing  this  film  between  the  Nicol  and 
the  cloud,  we  obtain,  instead  of  a  series  of  parallel  bands,  a 


262  FRAGMENTS  OF  SCIENCE. 

system  of  splendidly-colored  rings.  Precisely  the  same 
phenomena  are  observed  when  we  look  at  the  blue  firma- 
ment in  a  direction  perpendicular  to  the  solar  rays. 

We  have  thus  far  illuminated  our  artificial  sky  with 
ordinary  light.  We  will  now  examine  the  effects  produced 
when  the  light  which  illuminates  the  particles  is  itself 
polarized.  In  front  of  the  electric  lamp,  and  between  it 
and  the  experimental  tube,  is  placed  this  fine  Nicol's  prism, 
which  is  sufficiently  large  to  embrace  and  to  polarize  the 
entire  beam.  The  plane  of  vibration  of  the  light  now 
emergent  from  the  prism,  and  falling  upon  the  cloud,  is 
vertical ;  and  we  find  that  this  formless  aggregate  of  infini- 
tesimal particles,  without  definite  structure,  is  absolutely 
incompetent  to  scatter  the  light  upward  or  downward, 
while  it  freely  discharges  the  light  horizontally,  right  and 
left.  I  turn  the  polarizing  Nicol  so  as  to  render  the  plane 
of  vibration  horizontal ;  the  cloud  now  freely  scatters  the 
light  vertically  upward  and  downward,  but  it  is  absolutely 
incompetent  to  shed  a  ray  horizontally  to  the  right  or  left. 

Suppose  the  atmosphere  of  our  planet  to  be  surrounded 
by  an  envelope  impervious  to  light,  with  an  aperture  on 
the  sunward  side,  through  which  a  solar  beam  could  enter. 
Surrounded  on  all  sides  by  air  not  directly  illuminated,  the 
track  of  the  sunlight  would  resemble  that  of  the  electric 
beam  in  a  dark  space  filled  with  our  incipient  cloud.  The 
course  of  the  sunbeam  would  be  blue,  and  it  would  dis- 
charge laterally,  in  all  directions  round  it,  light  in  precisely 
the  same  polarized  condition  as  that  discharged  from  the 
incipient  cloud.  In  fact,  the  azure  revealed  by  the  sunbeam 
would  be  the  azure  of  such  a  cloud.  And  if,  instead  of 
permitting  the  ordinary  light  of  the  sun  to  enter  the  aper- 
ture, a  NicoPs  prism  were  placed  there,  which  should 
polarize  the  sunlight  on  its  entrance  into  our  atmosphere, 
the  particles  producing  the  color  of  the  sky  would  act 
precisely  like  those  of  our  incipient  cloud.  In  two  directions 


STRUCTURE  AND   LIGHT   OF   THE   SKY.  263 

we  should  have  the  solar  light  reflected ;  in  two  others  un- 
reflected.  In  fact,  out  of  such  a  solitary  beam,  traversing 
the  unilluminated  air,  we  should  be  able  to  extract  every 
effect  shown  by  our  incipient  cloud.  In  the  production  of 
such  clouds  we  virtually  carry  bits  of  the  sky  into  our 
laboratories,  and  obtain  with  them  all  the  effects  obtainable 
in  the  open  firmament  of  heaven. 

The  real  sky  is,  as  I  have  said,  less  perfect  than  our 
artificial  one  may  be  made.  For,  mingled  with  the  infini- 
tesimal particles  which  constitute  the  true  matter  of  the 
sky,  there  are  others  too  coarse  to  scatter  perfectly  po- 
larized light  at  right  angles  to  the  solar  beams.  Hence, 
when  the  brilliancy  of  the  sky  is  diminished  to  the  utter- 
most, there  is  still  a  residue  of  light;  the  extinction  is 
partial,  and  not  total,  as  in  the  case  of  our  incipient  cloud. 
Let  us  consider  this  matter.  The  perfect  polarization  can 
only  be  produced  by  excessively  minute  particles ;  imagine 
them  growing  gradually  larger  as  they  actually  do  in  our 
experiments.  The  extinction  by  the  Nicol  is  perfect  as 
long  as  the  polarization  is  complete.  But  what  would  you 
expect?  Manifestly,  that  after  a  time  the  polarization 
would  cease  to  be  perfect.  But  here  again  the  relation  of 
the  size  of  the  particles  to  the  size  of  the  waves  must  come 
into  play.  In  relation  to  the  blue  waves  the  particles  are 
larger  than  in  relation  to  the  red ;  the  blue  waves,  there- 
fore, will  be  the  first  liberated  from  a  condition  dependent 
on  the  smallness  of  the  particles.  They  will  first  escape 
from  the  trammels  of  polarization  ;  and  on  their  liberation 
they  exhibit  an  azure  far  purer  and  more  brilliant  than  that 
produced  by  the  first  precipitation  of  the  particles.  Could 
we  overarch  ourselves  with  a  sky  of  this  color  for  a  single 
day,  it  would  make  us  discontented  with  our  present  lack- 
lustre firmament  ever  afterward.  It  will  be  observed  that 
in  all  these  cases  reason  and  experiment  go  hand  in  hand, 
the  one  predicting,  the  other  verifying;  every  such  verift- 


264  FRAGMENTS  OF  SCIENCE. 

cation  lending  its  weight  of  proof  to  the  undulatory  theory 
on  which  the  predictions  are  founded. 

The  selenite  ring-system,  already  referred  to,  is  a  most 
delicate  reagent  for  the  detection  of  polarized  light.  When 
we  look  normally r,  or  perpendicularly,  at  an  incipient  cloud, 
the  colors  of  the  rings  are  most  vividly  developed,  a  dim- 
inution of  the  color  being  immediately  apparent  when 
the  incipient  cloud  is  regarded  obliquely.  But  let  us  con- 
tinue to  look  through  the  Nicol  and  selenite  normally  at 
the  cloud :  the  particles  augment  in  size,  the  cloud  becomes 
coarser  and  whiter,  the  strength  of  the  selenite  colors  be- 
coming gradually  feebler.  At  length  the  cloud  ceases  to 
discharge  polarized  light  along  the  normal,  and  then  the 
selenite  colors  entirely  disappear.  If,  now,  the  cloud  be  re- 
garded obliquely  the  colors  are  restored,  very  vividly,  if  not 
with  their  first  vividness  and  clearness.  Thus  the  cloud 
that  has  ceased  to  discharge  polarized  light  at  right  angles 
to  the  illuminating  beam,  pours  out  such  light  copiously  in 
oblique  directions.  The  direction  of  maximum  polariza- 
tion changes  with  the  texture  of  the  cloud. 

But  this  is  not  all ;  and  to  understand,  even  partially, 
what  remains,  a  word  must  be  said  regarding  the  appear- 
ance of  the  colors  of  our  plate  of  selenite.  If,  as  before 
stated,  the  plate  be  of  uniform  thickness,  its  hue  in  polar- 
ized light  is  uniform.  Suppose,  then,  that  by  arranging 
the  Nicol  the  color  of  the  plate  is  raised  to  its  maximum 
brilliancy,  and  suppose  the  color  produced  to  be  green"  on 
turning  the  Nicol  round  its  axis  the  green  becomes  fainter. 
When  the  angle  of  rotation  amounts  to  45°  the  color  dis- 
appears ;  we  then  pass  what  may  be  called  a  neutral  posi- 
tion, where  the  selenite  behaves,  not  as  a  crystal,  but  as  a 
bit  of  glass.  Continuing  the  rotation,  a  color  reappears, 
but  it  is  no  longer  green  but  red.  This  attains  its  maxi- 
mum at  a  distance  of  45°  from  the  neutral  position,  or,  in 
other  words,  at  a  distance  of  90°  from  the  position  which 


STRUCTURE  AND  LIGHT  OF  THE  SKY.  265 

showed  the  green  at  its  maximum.  At  a  further  distance 
of  45°  from  the  position  of  maximum  red,  the  color  disap- 
pears a  second  time.  We  have  there  a  second  neutral 
point,  beyond  which  the  green  comes  again  into  view,  at- 
taining its  maximum  brilliancy  at  the  end  of  a  rotation  of 
180°.  By  the  rotation  of  the  Nicol,  therefore,  through  an 
angle  of  90°,  we  produce  a  color  complementary  to  that 
with  which  we  started. 

As  may  be  inferred  from  this  result,  the  selenite  ring- 
system  changes  its  character  when  the  Nicol  is  turned. 
It  is  possible  to  have  the  centre  of  the  circle  dark,  the 
surrounding  rings  being  vividly  colored.  The  turning  of 
the  Nicol  through  an  angle  of  90°  renders  the  centre  bright, 
while  every  point  occupied  by  a  certain  color  in  the  first 
instance  is  occupied  by  the  complement  of  that  color  in  the 
second.  By  curious  internal  actions,  not  here  to  be  de- 
scribed, the  cloud  in  our  experimental  tube  sometimes 
divides  itself  into  sections  of  different  textures.  Some  sec- 
tions are  coarser  than  others,  while  it  often  happens  that 
some  are  iridescent  to  the  naked  eye,  and  others  not. 
Looking  normally  at  such  a  cloud  through  the  selenite  and 
Nicol,  it  often  happens  that  in  passing  from  section  to  sec- 
tion the  whole  character  of  the  ring-system  is  changed. 
You  start  with  a  section  producing  a  dark  centre  and  a 
corresponding  system  of  rings  ;  you  pass  through  a  neutral 
point  to  another  section  and  find  there  the  centre  bright, 
and  each  of  the  first  rings  displaced  by  one  of  the  comple- 
mentary color.  Sometimes  as  many  as  four  such  rever- 
sions occur  in  the  cloud  of  an  experimental  tube  a  yard 
long.  Now,  the  changes  here  indicated  mean  that  in  passing 
from  section  to  section  of  the  cloud  the  plane  of  vibration 
of  the  polarized  light  turns  suddenly  through  an  angle  of 
90° ;  this  change  being  entirely  due  to  the  different  texture 
of  the  two  parts  of  the  cloud. 

You  will  now  be  able  to  understand,  as  far  as  it  is  cat 
12 


266  FRAGMENTS  OF  SCIENCE. 

pable  of  being  understood,  a  very  beautiful  effect  which, 
under  favorable  circumstances,  might  be  observed  in  our 
atmosphere.  This  experimental  tube  contains  an  inch  of 
the  iodide-of-allyl  vapor,  the  remaining  29  inches  necessary 
to  fill  the  tube  being  air,  which  has  bubbled  through  aque- 
ous hydrochloric  acid.  Besides,  therefore,  the  vapor  of 
iodide  of  allyl,  we  have  those  of  water  and  of  acid  within 
the  tube.  The  light  has  been  acting  on  the  mixture  for 
some  time,  a  beautiful  incipient  blue  cloud  being  formed.  As 
before  stated,  the  "  incipient  cloud  "  is  wholly  different  in 
texture  and  optical  properties  from  an  ordinary  cloud ;  but 
it  is  possible  to  precipitate  in  the  midst  of  the  azure  the 
aqueous  vapor  so  as  to  cause  it  to  form  in  the  tube  a  cloud 
similar  to  the  clouds  of  our  atmosphere.  An  exhausted 
vessel  of  about  one-third  of  the  capacity  of  the  experi- 
mental tube  is  connected  with  it,  the  passage  uniting  both 
being  closed  by  a  stop-cock.  On  opening  this  cock  the 
mixed  air  and  vapor  rush  from  the  experimental  tube  into 
the  empty  vessel ;  and,  in  consequence  of  the  chilling  due 
to  rarefaction,  the  vapor  in  the  experimental  tube  is  pre- 
cipitated as  a  true  cloud.  What  is  the  result  ?  Instantly 
the  centre  of  the  system  of  colored  rings  becomes  bright, 
and  the  whole  series  of  colors  corresponding  to  definite  ra- 
dial distances,  complementary:  While  you  continue  to 
look  at  the  cloud,  it  gradually  melts  away  as  an  atmos- 
pheric cloud  might  do  in  the  azure  of  heaven.  And  there 
is  our  azure  also  remaining  behind.  The  coarser  cloud 
seems  drawn  aside  like  a  veil,  the  blue  reappears,  the  first 
ring-system,  with  its  dark  centre  and  correspondingly  col- 
ored circles,  being  restored. 

Thus  patiently  you  have  accompanied  me  over  a  piece 
of  exceedingly  difficult  ground ;  and  I  think,  as  a  prudent 
guide,  we  ought  to  halt .  upon  the  eminence  we  have  now 
attained.  We  might  go  higher,  but  the  bowlders  begin 
here  to  be  very  rough.  At  a  future  day  we  shall,  I  doubt 


STRUCTURE  AND  LIGHT  OF  THE  SKY.  267 

not,  be  able  to  overcome  this  difficulty,  and  to  reach  to- 
gether a  greater  elevation. 


THE  SKY  OF  THE  ALPS. 

THE  vision  of  an  object  always  implies  a  differential 
action  on  the  retina  of  the  observer.  The  object  is  dis- 
tinguished from  surrounding  space  by  its  excess  or  defect 
of  light  in  relation  to  that  space.  By  altering  the  illumi- 
nation, either  of  the  object  itself  or  of  its  environment,  we 
alter  the  appearance  of  the  object.  Take  the  case  of  clouds 
floating  in  the  atmosphere  with  patches  of  blue  between 
them.  Any  thing  that  changes  the  illumination  of  either 
alters  the  appearance  of  both,  that  appearance  depending, 
as  stated,  upon  differential  action.  Now  the  light  of  the 
sky  being  polarized,  may,  as  the  reader  of  the  foregoing 
pages  knows,  be  in  great  part  quenched  by  a  Nicol's 
prism,  while  the  light  of  a  cloud,  being  unpolarized,  cannot 
be  thus  extinguished.  Hence  the  possibility  of  very  re- 
markable variations,  not  only  in  the  aspect  of  the  firma- 
ment, which  is  really  changed,  but  also  in  the  aspect  of  the 
clouds  which  have  that  firmament  as  a  background.  It  is 
possible,  for  example,  to  choose  clouds  of  such  a  depth  of 
shade  that  when  the  Nicol  quenches  the  light  behind  them, 
they  shall  vanish,  being  undistinguishable  from  the  residual 
dull  tint  which  outlives  the  extinction  of  the  brilliance  of 
the  sky.  A  cloud  less  deeply  shaded,  but  still  deep  enough, 
when  viewed  with  the  naked  eye,  to  appear  dark  on  a 
bright  ground,  is  suddenly  changed  to  a  white  cloud  on  a 
dark  ground  by  the  quenching  of  the  sky  behind  it.  When 
a  reddish  cloud  at  sunset  chances  to  float  in  the  region  of 
maximum  polarization,  the  quenching  of  the  sky  behind  it 
causes  it  to  flash  with  a  brighter  crimson.  Last  Easter  eve 
the  Dartmoor  sky,  which  had  just  been  cleansed  by  a  snow- 


268  FRAGMENTS  OF  SCIENCE. 

storm,  wore  a  very  wild  appearance.  Round  the  horizon  it 
was  of  steely  brilliancy,  while  reddish  cumuli  and  cirri 
floated  southward.  When  the  sky  was  quenched  behind 
them  these  floating  masses  seemed  like  dull  embers  sud- 
denly blown  upon ;  they  brightened  like  a  fire.  In  the 
Alps  we  have  the  most  magnificent  examples  of  crimson 
clouds  and  snows,  so  that  the  effects  just  referred  to  may 
be  here  studied  under  the  best  possible  conditions.  On 
August  23,  1869,  the  evening  Alpenglow  was  very  fine, 
though  it  did  not  reach  its  maximum  depth  and  splendor. 
Toward  sunset  I  walked  up  the  slopes  to  obtain  a  better 
view  of  the  Weisshorn.  The  side  of  the  peak  seen  from  the 
Bel  Alp,  being  turned  from  the  sun,  was  tinted  mauve  ; 
but  I  wished  to  see  one  of  the  rose-colored  buttresses  of  the 
mountain.  Such  was  visible  from  a  point  a  few  hundred 
feet  above  the  hotel.  The  Matterhorn  also,  though  for  the 
most  part  in  shade,  had  a  crimson  projection,  while  a  deep 
ruddy  red  lingered  along  its  western  shoulder.  Four  dis- 
tinct peaks  and  buttresses  of  the  Dom,  in  addition  to  its 
dominant  head — all  covered  with  pure  snow — were  red- 
dened by  the  light  of  sunset.  The  shoulder  of  the  Alphu- 
bel  was  similarly  colored,  while  the  great  mass  of  the  Flet- 
schorn  was  all  a-glow,  and  so  was  the  snowy  spine  of  the 
Monte  Leone. 

Looking  at  the  Weisshorn  through  the  Nicol,  the  glow 
of  its  protuberance  was  strong  or  weak  according  to  the 
position  of  the  prism.  The  summit  also  underwent  a 
change.  In  one  position  of  the  prism  it  exhibited  a  pale 
white  against  a  dark  background ;  in  the  rectangular  posi- 
tion, it  was  a  dark  mauve  against  a  light  background.  The 
red  of  the  Matterhorn  changed  in  a  similar  manner ;  but 
the  whole  mountain  also  passed  through  striking  changes 
of  definition.  The  air  at  the  time  was  filled  with  a  silvery 
haze,  in  which  the  Matterhorn  almost  disappeared.  This 
could  be  wholly  quenched  by  the  Nicol,  and  then  the 


THE  SKY  OF  THE  ALPS.  269 

mountain  sprang  forth  with  astonishing  solidity  and  detach- 
ment from  the  surrounding  air.  The  changes  of  the  Dom 
were  still  more  wonderful.  A  vast  amount  of  light  could 
be  removed  from  the  sky  behind  it,  for  it  occupied  the  po- 
sition of  maximum  polarization.  By  a  little  practice  with 
the  Nicol  it  was  easy  to  render  the  extinction  of  the  light, 
or  its  restoration,  almost  instantaneous.  When  the  sky  was 
quenched,  the  four  minor  peaks  and  buttresses,  and  the 
summit  of  the  Dom,  together  with  the  shoulder  of  the  Al- 
phubel,  glowed  as  if  set  suddenly  on  fire.  This  was  imme- 
diately dimmed  by  turning  the  Nicol  through  an  angle  of 
90°.  It  was  not  the  stoppage  of  the  light  of  the  sky  behind 
the  mountains  alone  which  produced  this  startling  effect ; 
the  air  between  them  and  me  was  highly  opalescent,  and 
the  quenching  of  this  intermediate  glare  augmented  re- 
markably the  distinctness  of  the  mountains. 

On  the  morning  of  August  24th  similar  effects  were  fine- 
ly shown.  At  10  A.  M.  all  three  mountains,  the  Dom,  the 
Matterhorn,  and  the  Weisshorn,  were  powerfully  affected 
by  the  Nicol.  But  in  this  instance  also  the  line  drawn  to 
the  Dom  being  accurately  perpendicular  to  the  direction  of 
the  solar  shadows,  and  consequently  very  nearly  perpen- 
dicular to  the  solar  beams,  the  effects  on  this  mountain  were 
most  striking.  The  gray  summit  of  the  Matterhorn  at  the 
same  time  could  scarcely  be  distinguished  from  the  opales- 
cent haze  around  it ;  but  when  the  Nicol  quenched  the 
haze,  the  summit  became  instantly  isolated,  and  stood  out 
in  bold  definition.  It  is  to  be  remembered  that  in  the  pro- 
duction of  these  effects  the  only  things  changed  are  the 
sky  behind  and  the  luminous  haze  in  front  of  the  moun- 
tains ;  that  these  are  changed  because  the  light  emitted 
from  the  sky  and  from  the  haze  is  plane  polarized  light,1 
and  that  the  light  from  the  snows  and  from  the  mountains 
being  sensibly  unpolarized,  is  not  directly  affected  by  the 
1  Defined  at  page  255. 


270  FRAGMENTS  OF  SCIENCE. 

Nicol.  It  will  also  be  understood  that  it  is  not  the  interposi- 
tion of  the  haze  as  an  opaque  body  that  renders  the  moun- 
tains indistinct,  but  that  it  is  the  light  of  the  haze  which 
dims  and  bewilders  the  eye,  and  thus  weakens  the  defini- 
tion of  objects  seen  through  it. 

The  results  have  a  direct  bearing  upon  what  artists  call 
"  aerial  perspective."  As  we  look  from  the  summit  of  the 
Aletschhorn,  or  from  a  lower  elevation,  at  the  serried  crowd 
of  peaks,  especially  if  the  mountains  be  darkly  colored — 
covered  with  pines,  for  example — every  peak  and  ridge  is 
separated  from  the  mountains  behind  it  by  a  thin  blue  haze 
which  renders  the  relations  of  the  mountains  as  to  distance 
unmistakable.  When  this  haze  is  regarded  through  the 
Nicol  perpendicular  to  the  sun's  rays,  it  is  in  many  cases 
wholly  quenched,  because  the  light  which  it  emits  in  this 
direction  is  wholly  polarized.  When  this  happens,  aerial 
perspective  is  abolished,  and  mountains  very  differently  dis- 
tant appear  to  rise  in  the  same  vertical  plane.  Close  to  the 
Bel  Alp,  for  instance,  is  the  gorge  of  the  Massa,  and  beyond 
the  gorge  is  a  high  ridge  darkened  by  pines.  This  ridge 
may  be  projected  upon  the  dark  slopes  at  the  opposite  side 
of  the  Rhone  valley,  and  between  both  we  have  the  blue 
haze  referred  to,  throwing  the  distant  mountains  far  away. 
But  at  certain  hours  of  the  day  this  haze  may  be  quenched, 
and  then  the  Massa  ridge  and  the  mountains  beyond  the 
Rhone  seem  almost  equally  distant  from  the  eye.  The  one 
appears,  as  it  were,  a  vertical  continuation  of  the  other. 
The  haze  varies  with  the  temperature  and  humidity  of  the 
atmosphere.  At  certain  times  and  places  it  is  almost  as 
blue  as  the  sky  itself ;  but  to  see  its  color,  the  attention 
must  be  withdrawn  from  the  mountains  and  from  the  trees 
which  cover  them.  In  point  of  fact,  the  haze  is  a  piece  of 
more  or  less  perfect  sky ;  it  is  produced  in  the  same  man- 
ner, and  is  subject  to  the  same  laws,  as  the  firmament  it- 
self. We  live  in  the  sky,  not  under  it. 


THE   SKY  OF  THE  ALPS.  271 

These  points  were  further  elucidated  by  the  deportment 
of  the  selenite  plate,  with  which  the  readers  of  the  fore- 
going discourse  are  already  acquainted.  On  some  of  the 
sunny  days  of  August  the  haze  in  the  valley  of  the  Rhone, 
as  looked  at  from  the  Bel  Alp,  was  very  remarkable.  Tow- 
ward  evening  the  sky  above  the  mountains  opposite  to  my 
place  of  observation  yielded  a  series  of  the  most  splendidly- 
colored  iris-rings ;  but  on  lowering  the  selenite  until  it  had 
the  darkness  of  the  pines  at  the  opposite  side  of  the  Rhone 
valley,  instead  of  the  darkness  of  space  as  a  background, 
the  colors  were  not  much  diminished  in  brilliancy.  I  should 
estimate  the  distance  across  the  valley,  as  the  crow  flies,  to 
the  opposite  mountains,  at  nine  miles ;  so  that  a  body  of 
air  nine  miles  thick  can,  under  favorable  circumstances, 
produce  chromatic  effects  of  polarization  almost  as  vivid  as 
those  produced  by  the  sky  itself. 

Again  :  the  light  of  a  landscape,  as  of  most  other  things, 
consists  of  two  parts:  the  one  part  comes  purely  from 
superficial  reflection,  and  this  light  is  always  of  the  same 
color  as  that  which  falls  upon  the  landscape ;  the  other 
part  comes  to  us  from  a  certain  depth  within  the  objects 
which  compose  the  landscape,  and  it  is  this  portion  of  the 
total  light  which  gives  these  objects  their  distinctive 
colors.  The  white  light  of  the  sun  enters  all  substances  to 
a  certain  depth,  and  is  partially  ejected  by  internal  reflec- 
tion ;  each  distinct  substance  absorbing  and  reflecting  the 
light  in  accordance  with  the  laws  of  its  own  molecular  con- 
stitution. Thus  the  solar  light  is  sifted  by  the  landscape, 
which  appears  in  such  colors  and  variations  of  color  as, 
after  the  sifting  process,  reach  the  observer's  eye.  Thus 
the  bright  green  of  grass,  or  the  darker  color  proper  to  the 
pine,  never  comes  to  us  alone,  but  is  always  mingled  with 
an  amount  of  really  foreign  light  derived  from  superficial 
reflection.  A  certain  hard  brilliancy  is  conferred  upon  the 
woods  and  meadows  by  this  superficially-reflected  light. 


272  FRAGMENTS  OF  SCIENCE. 

Under  certain  circumstances,  it  may  be  quenched  by  a 
Nicol's  prism,  and  we  then  obtain  the  true  color  of  the  grass 
and  foliage.  Trees  and  meadows  thus  regarded  exhibit  a 
richness  and  softness  of  tint  which  they  never  show  as  long 
as  the  superficial  light  is  permitted  to  mingle  with  the  true 
interior  emission.  The  needles  of  the  pines  show  this  effect 
very  well,  large-leaved  trees  still  better ;  while  a  glimmer- 
ing field  of  maize  exhibits  the  most  extraordinary  variations 
when  looked  at  through  the  rotating  Nicol. 

Thoughts  and  questions  like  those  here  referred  to  took 
me,  in  August,  1869,  to  the  top  of  the  Aletschhorn.  The 
effects  described  in  the  foregoing  paragraphs  were  for  the 
most  part  reproduced  in  the  summit  of  the  mountain.  I 
scanned  the  whole  of  the  sky  with  my  Nicol.  Both  alone 
and  in  conjunction  with  the  selenite  it  pronounced  the  per- 
pendicular to  the  solar  beams  to  be  the  direction  of  maxi- 
mum polarization.  But  at  no  portion  of  the  firmament  was 
the  polarization  complete.  The  artificial  sky  produced  in 
the  experiments  recorded  in  the  preceding  discourse  could, 
in  this  respect,  be  rendered  more  perfect  than  the  natural 
one  ;  while  the  gorgeous  "  residual  blue  "  which  makes  its 
appearance  when  the  polarization  of  the  artificial  sky  ceases 
to  be  perfect,  was  strongly  contrasted  with  the  lack-lustre 
hue  which,  in  the  case  of  the  firmament,  outlived  the  ex- 
tinction of  the  brilliance.  With  certain  substances,  how- 
ever, artificially  treated,  this  dull  residue  may  also  be  ob- 
tained. 

All  along  the  arc  from  the  Matterhorn  to  Mont  Blanc 
the  light  of  the  sky  immediately  above  the  mountains  was 
powerfully  acted  upon  by  the  Nicol.  In  some  cases  the 
variations  of  intensity  were  astonishing.  I  have  already 
said  that  a  little  practice  enables  the  observer  to  shift  the 
Nicol  from  one  position  to  another  so  rapidly  as  to  render 
the  alternate  extinction  and  restoration  of  the  light  imme- 
diate. When  this  was  done  along  the  arc  to  which  I  have 


THE  SKY  OF  THE  ALPS.  273 

referred,  the  alternations  of  light  and  darkness  resembled 
the  play  of  sheet-lightning  behind  the  mountains.  My 
notes  state  that  there  was  an  element  of  awe  connected 
with  the  suddenness  with  which  the  mighty  masses,  ranged 
along  the  line  referred  to,  changed  their  aspect  and  defi- 
nition under  the  operation  of  the  prism. 


JLibrary* 

California 


XI. 
DUST  AND  DISEASE. 

A  DISCOURSE. 

DELIVEEED  IN  THE  ROYAL  INSTITUTION  OP  GEEAT  BRITAIN. 

January  21,  1870.      With  Additions. 


"  Tout  rniasme  contagieux  ales  proprictcs,  1s  de  reproduire  son  ana- 
logue dans  une  maladie  qu'il  a  occasionnee ;  2°  de  se  repandre  et  dc 
s'entendre  a  1'infini,  en  vertu  de  ce  developpement  secondaire,  c'est-a- 
dire,  aussi  longtemps  qu'il  existe  unematiere  propre  a  recevoir  le  miasme, 
et  en  a  produire  un  nouveau.  Ces  deux  proprietcs  lui  sont  communes 
avec  les  germes  des  animaux  et  des  plantes. 

HlLDEBRAND. 


XL 

ON  DUST  AND   DISEASE. 

Experiments  on  Dusty  Air. 

SOLAR  light  in  passing  through  a  dark  room  reveals  its 
track  by  illuminating  the  dust  floating  in  the  air.  "  The 
sun,"  says  Daniel  Culverwell,  "  discovers  atonies,  though 
they  be  invisible  by  candle-light,  and  makes  them  dance 
naked  in  his  beams."  1 

In  my  researches  on  the  decomposition  of  vapors  by 
light,  I  was  compelled  to  remove  these  "  atomes  "  and  this 
dust.  It  was  essential  that  the  space  containing  the  vapors 
should  embrace  no  visible  thing ;  that  no  substance  capable 
of  scattering  the  light  in  the  slightest  sensible  degree 
should,  at  the  outset  of  an  experiment,  be  found  in  the  "  ex- 
perimental tube  "  traversed  by  the  luminous  beam. 

For  a  long  time  I  was  troubled  by  the  appearance  there 
of  floating  dust,  which  though  invisible  in  diffuse  daylight 
was  at  once  revealed  by  a  powerfully-condensed  beam.  Two 
tubes  were  placed  in  succession  in  the  path  of  the  air :  the 
one  containing  fragments  of  glass  wetted  with  concentrated 
sulphuric  acid ;  the  other,  fragments  of  marble  wetted  with 
a  strong  solution  of  caustic  potash.  To  my  astonishment 
the  dust  passed  through  both.  The  air  of  the  Royal  Insti- 
tution sent  through  these  tubes  at  a  rate  sufficiently  slow 

1  On  a  day  of  transient  shadows  there  is  something  almost  magical  in 
the  rise  and  dissolution  of  the  luminous  beams  among  the  scaffolding 
poles  of  the  Royal  Albert  Hall. 


278  FRAGMENTS  OF  SCIENCE. 

to  dry  it,  and  to  remove  its  carbonic  acid,  carried  into  the 
experimental  tube  a  considerable  amount  of  mechanically 
suspended  matter,  which  was  illuminated  when  the  beam 
passed  through  the  tube.  The  effect  was  substantially  the 
same  when  the  air  was  permitted  to  bubble  through  the 
liquid  acid  and  through  the  solution  of  potash. 

Thus,  on  October  5, 1868,  successive  charges  of  air  were 
admitted  through  the  potash  and  sulphuric  acid  into  the  ex- 
hausted experimental  tube.  Prior  to  the  admission  of  the 
air  the  tube  was  optically  empty ;  it  contained  nothing 
competent  to  scatter  the  light.  After  the  air  had  entered 
the  tube,  the  conical  track  of  the  electric  beam  was  in  all 
cases  clearly  revealed.  This,  indeed,  was  a  daily  observa- 
tion at  the  time  to  which  I  now  refer. 

I  tried  to  intercept  this  floating  matter  in  various  ways ; 
and  on  the  day  just  mentioned,  prior  to  sending  the  air 
through  the  drying  apparatus,  I  carefully  permitted  it  to 
pass  over  the  tip  of  a  spirit-lamp  flame.  The  floating  mat- 
ter no  longer  appeared,  having  been  burnt  up  by  the  flame. 
It  was,  therefore,  of  organic  origin.  I  was  by  no  means 
prepared  for  this  result ;  for  I  had  thought  that  the  dust  of 
our  air  was,  in  great  part,  inorganic  and  non-combustible. 

I  had  constructed  a  small  gas-furnace,  now  much  em- 
ployed by  chemists,  containing  a  platinum  tube,  which 
could  be  heated  to  vivid  redness.1  The  tube  contained  a 
roll  of  platinum  gauze,  which,  while  it  permitted  the  air  to 
pass  through  it,  insured  the  practical  contact  of  the  dust 
with  the  incandescent  metal.  The  air  of  the  laboratory 
was  permitted  to  enter  the  experimental  tube,  sometimes 
through  the  cold,  and  sometimes  through  the  heated,  tube 
of  platinum.  The  rapidity  of  admission  was  also  varied. 
In  the  first  column  of  the  following  table  the  quantity  of 
air  operated  on  is  expressed  by  the  number  of  inches  which 
the  mercury  gauge  of  the  air-pump  sank  when  the  air  en- 

1  Pasteur  was,  I  believe,  the  first  to  employ  such  a  tube. 


DUST  AND   DISEASE.  279 

tered.  In  the  second  column  the  condition  of  the  platinum 
tube  is  mentioned,  and  in  the  third  the  state  of  the  air 
which  had  entered  the  experimental  tube. 

Quantity  of  Air.  State  of  Platinum  Tube.         State  of  Experimental  Tube. 

15  inches Cold Full  of  particles. 

15      "      Red  hot Optically  empty. 

The  phrase  "  optically  empty  "  shows  that  when  the  con- 
ditions of  perfect  combustion  were  present,  the  floating 
matter  totally  disappeared.  It  was  wholly  burnt  up,  leav- 
ing no  sensible  residue.  The  experiment  was  repeated 
many  times,  with  the  same  invariable  result. 

The  whole  of  the  visible  particles  floating  in  the  air  of 
London  rooms  being  thus  proved  to  be  of  organic  origin,1 
I  sought  to  burn  them  up  at  the  focus  of  a  concave  re- 
flector. One  of  the  powerfully  convergent  mirrors  em- 
ployed in  my  experiments  on  combustion  by  dark  rays  was 
here  made  use  of,  but  I  failed  in  the  attempt.  Doubtless 
the  floating  particles  are  in  part  transparent  to  radiant  heat, 
and  are  so  far  incombustible  by  such  heat.  Their  rapid 
motion  through  the  focus  also  aids  their  escape.  They  do 
not  linger  there  sufficiently  long  to  be  consumed.  A  flame 
it  was  evident  would  burn  them  up,  but  I  at  first  thought 
the  presence  of  the  flame  would  mask  its  own  action  among 
the  particles. 

1  According  to  an  analysis  kindly  furnished  to  me  by  Dr.  Percy,  the  dust 
collected  from  the  walk  of  the  British  Museum  contains  fully  50  per  cent, 
of  inorganic  matter.  I  have  every  confidence  in  the  results  of  this  dis- 
tinguished chemist ;  they  show  that  the  floating  dust  of  our  rooms  is,  as  it 
were,  winnowed  from  the  heavier  matter.  As  bearing  directly  upon  this 
point,  I  may  quote  the  following  passage  from  Pasteur :  "  Mais  ici  se 
presente  une  remarque :  la  poussiere  que  1'on  trouve  a  la  surface  de  tous 
les  corps  est  soumise  constamment  a  des  courants  d'air,  qui  doivent  sou- 
lever  ses  particules  les  plus  legeres,  au  nombre  desquelles  se  trouvent,  sans 
doute,  de  preference  les  corpuscules  organises,  oaufs  ou  spores,  moins 
lourds  generalement  que  les  particules  minerales." 


280  FRAGMENTS  OF  SCIENCE. 

In  a  cylindrical  beam,  which  strongly  illuminated  the 
dust  of  the  laboratory,  was  placed  an  ignited  spirit-lamp. 
Mingling  with  the  flame,  and  round  its  rim,  were  seen 
curious  wreaths  of  darkness  resembling  an  intensely-black 
smoke.  On  lowering  the  flame  below  the  beam  the  same 
dark  masses  stormed  upward.  They  were  at  times  blacker 
than  the  blackest  smoke  that  I  have  ever  seen  issuing  from 
the  funnel  of  a  steamer ;  and  their  resemblance  to  smoke 
was  so  perfect  as  to  lead  the  most  practised  observer  to 
conclude  that  the  apparently-pure  flame  of  the  alcohol-lamp 
required  but  a  beam  of  sufficient  intensity  to  reveal  its 
clouds  of  liberated  carbon. 

But  is  the  blackness  smoke  ?  This  question  presented 
itself  in  a  moment.  A  red-hot  poker  was  placed  under- 
neath the  beam,  and  from  it  the  black  wreaths  also  as- 
cended. A  large  hydrogen-flame  was  next  employed,  and 
it  produced  those  whirling  masses  of  darkness  far  more 
copiously  than  either  the  spirit-flame  or  poker.  Smoke  was 
therefore  out  of  the  question. 

What,  then,  was  the  blackness  ?  It  was  simply  that  of 
stellar  space ;  that  is  to  say,  blackness  resulting  from  the 
absence  from  the  track  of  the  beam  of  all  matter  competent 
to  scatter  its  light.  When  the  flame  was  placed  below  the 
beam,  the  floating  matter  was  destroyed  in  situ  •  and  the 
air,  freed  from  this  matter,  rose  into  the  beam,  jostled  aside 
the  illuminated  particles,  and  substituted  for  their  light  the 
darkness  due  to  its  own  perfect  transparency.  Nothing 
could  more  forcibly  illustrate  the  invisibility  of  the  agent 
which  renders  all  things  visible.  The  beam  crossed,  un- 
seen, the  black  chasm  formed  by  the  transparent  air,  while 
at  both  sides  of  the  gap  the  thick-strewn  particles  shone 
out  like  a  luminous  solid  under  the  powerful  illumina- 
tion. 

But  here  a  rather  perplexing  difficulty  meets  us.  It  is 
not  necessary  to  burn  the  particles  to  produce  a  stream  of 


DUST  AND  DISEASE.  281 

darkness.  Without  actual  combustion,  currents  may  be 
generated  which  shall  exclude  the  floating  matter,  and 
therefore  appear  dark  amid  the  surrounding  brightness.  I 
noticed  this  effect  first  on  placing  a  red-hot  copper  ball  be- 
low the  beam,  and  permitting  it  to  remain  there  until  its 
temperature  had  fallen  below  that  of  boiling  water.  The 
dark  currents,  though  much  enfeebled,  were  still  produced. 
They  may  also  be  produced  by  a  flask  filled  with  hot 
water. 

To  study  this  effect  a  platinum  wire  was  stretched 
across  the  beam,  the  two  ends  of  the  wire  being  connected 
with  the  two  poles  of  a  voltaic  battery.  To  regulate  the 
strength  of  the  current  a  rheostat  was  placed  in  the  circuit. 
Beginning  with  a  feeble  current  the  temperature  of  the 
wire  was  gradually  augmented ;  but,  before  it  reached  the 
heat  of  ignition,  a  flat  stream  of  air  rose  from  it,  which 
when  looked  at  edgeways  appeared  darker  and  sharper  than 
one  of  the  blackest  lines  of  Fraunhofer  in  the  solar  spec- 
trum. Bight  and  left  of  this  dark  vertical  band  the  float- 
ing matter  rose"  upward,  bounding  definitely  the  non-lumi- 
nous stream  of  air.  What  is  the  explanation?  Simply 
this  :  The  hot  wire  rarefied  the  air  in  contact  with  it,  but 
it  did  not  equally  lighten  the  floating  matter.  The  con- 
vection current  of  pure  air  therefore  passed  upward  among 
the,  inert  particles,  dragging  them  after  it  right  and  left,  but 
forming  between  them  an  impassable  black  partition.  This 
elementary  experiment  enables  us  to  render  an  account  of 
the  dark  currents  produced  by  bodies  at  a  temperature  be- 
low that  of  combustion. 

When  the  wire  is  white  hot,  it  sends  up  a  band  of  in- 
tense darkness.  This,  I  say,  is  due  to  the  destruction  of 
the  floating  matter.  But  even  when  its  temperature  does 
not  exceed  that  of  boiling  water,  the  wire  produces  a  dark 
ascending  current.  This,  I  say,  is  due  to  the  distribution 
of  the  floating  matter.  Imagine  the  wire  clasped  by  the 


282  FKAGMENTS  OF  SCIENCE. 

mote-filled  air.  My  idea  is  that  it  heats  the  air  and  lightens 
it,  without  in  the  same  degree  lightening  the  floating  mat- 
ter. The  tendency,  therefore,  is  to  start  a  current  of  clean 
air  through  the  mote-filled  air.  Figure  the  motion  of  the 
air  all  round  the  wire.  Looking  at  its  transverse  section 
we  should  see  the  air  at  the  bottom  of  the  wire  bending 
round  it  right  and  left  in  two  branch-currents,  ascend- 
ing its  sides  and  turning  to  fill  the^  partial  vacuum  created 
above  the  wire.  Now  as  each  new  supply  of  air,  filled  with 
its  motes,  comes  in  contact  with  the  hot  wire,  the  clean 
air,  as  just  stated,  is  first  started  through  the  inert  motes. 
They  are  dragged  after  it,  but  there  is  a  fringe  of  cleansed 
air  in  advance  of  the  motes.  The  two  purified  fringes  of 
the  two  branch-currents  unite  above  the  wire,  and,  keep- 
ing the  motes  that  once  belonged  to  them  right  and  left, 
they  form  by  their  union  the  dark  band  observed  in  the 
experiment.  This  process  is  incessant.  Always  the  mo- 
ment the  mote-filled  air  touches  the  wire  this  distribution 
is  effected,  a  permanent  dark  band  being  thus  produced. 
Could  the  air  and  the  particles  under  the  wire  pass  through 
its  mass  we  should  have  a  vertical  current  of  particles,  but 
no  dark  band.  For  here,  though  the  motes  would  be  left 
behind  at  starting,  they  would  hotly  follow  the  ascending 
current  and  thus  abolish  the  darkness. 

It  has  been  said  that  when  the  platinum  wire  is  intensely 
heated,  the  floating  matter  is  not  only  distributed,  but  de- 
stroyed. Let  this  be  proved.  I  stretched  a  wire  about  4 
inches  long  through  the  air  of  an  ordinary  glass  shade,  rest- 
ing on  its  stand.  Its  lower  rim  rested  on  cotton-wool,  which 
also  surrounded  the  rim.  The  wire  was  raised  to  a  white 
heat  by  an  electric  current.  The  air  expanded,  and  some 
of  it  was  forced  through  the  cotton-wool,  while,  when  the 
current  was  interrupted  and  the  air  within  the  shade  cooled, 
the  expelled  air  in  its  return  did  not  carry  motes  along  with 
it.  At  the  beginning  of  this  experiment  the  shade  was 


DUST  AND  DISEASE.  283 

charged  with  floating  matter ;  at  the  end  of  half  an  hour  it 
was  optically  empty. 

A  second  experiment  was  thus  arranged :  on  the  wooden 
base  of  a  cubical  glass  shade,  measuring  11|-  inches  a  side, 
upright  supports  were  fixed,  and  from  one  support  to  the 
other  38  inches  of  platinum  wire  were  stretched  in  four 
parallel  lines.  The  ends  of  the  platinum  wire  were  soldered 
to  two  stout  copper  wires,  which  passed  through  the  base 
of  the  shade  and  could  be  connected  with  a  battery.  As 
in  the  last  experiment,  the  shade  rested  upon  cotton-wool. 
A  beam  sent  through  the  shade  revealed  the  suspended 
matter.  The  platinum  wire  was  then  raised  to  whiteness. 
In  iive  minutes  there  was  a  sensible  diminution  of  the  mat- 
ter, and  in  ten  minutes  it  was  totally  consumed.  This 
proves  that  when  the  platinum  wire  is  sufficiently  heated, 
the  floating  matter,  instead  of  being  distributed,  is  destroyed. 

But  is  not  the  matter  really  of  a  character  which  permits 
of  its  destruction  by  the  moderately-heated  platinum  wire  ? 
Here  is  the  reply : 

1.  A  platinum  tube,  with  its  plug  of  platinum  gauze, 
was  connected  with  an  experimental  tube,  through  which  a 
powerful  beam  could  be  sent  from  an  electric  lamp  placed 
at  its  end.     The  platinum  tube  was  heated  till  it  glowed 
feebly  but  distinctly  in  the  dark.     The  experimental  tube 
was  exhausted,  and  then  filled  with  air  which  had  passed 
through  the  red-hot  tube.     A  considerable  amount  of  float- 
ing matter  which  had  escaped  combustion  was  revealed  by 
the  electric  beam. 

2.  The  tube  was  raised  to  brighter  redness  and  the  air 
permitted  to  pass  slowly  through  it.     Though  diminished 
in  quantity,  a  certain  amount  of  floating  matter  passed  into 
the  exhausted  experimental  tube. 

3.  The   platinum    tube  was    rendered    still   hotter ;    a 
barely  perceptible  trace  of  the  floating  matter  now  passed 
through  it. 


284  FRAGMENTS  OF  SCIENCE. 

4.  The  experiment  was  repeated,  with  the  difference 
that  the  air  was  sent  more  slowly  through  the  red-hot  tube. 
The  floating  matter  was  totally  destroyed. 

5.  The  platinum  tube  was  now  lowered  until  it  bordered 
upon  a  visible  red  heat.     The  air  sent  through  it  still  more 
slowly  than  in  the  last  experiment  carried  with  it  a  cloud 
of  floating  matter. 

If,  then,  the  suspended  matter  is  destroyed  by  a  bright- 
red  heat,  much  more  is  it  destroyed  by  a  flame,  whose  tem- 
perature is  vastly  higher  than  any  here  employed.  So  that 
the  blackness  introduced  into  a  luminous  beam  where  a 
flame  is  placed  beneath  it  is  due,  as  stated,  to  the  destruc- 
tion of  the  suspended  matter.  At  a  dull-red  heat,  how- 
ever, and  still  more  when  only  on  the  verge  of  redness,  the 
platinum  tube  permitted  the  motes  to  pass  freely.  In  the 
latter  case  the  temperature  was  800°  or  900°  Fahrenheit. 
This  was  unable  to  destroy  the  suspended  matter ;  much 
less,  therefore,  would  a  platinum  wire  heated  to  212°  be 
competent  to  do  so.  Such  a  wire  can  only  distribute  the 
matter,  not  destroy  it. 

The  floating  dust  is  revealed  by  intense  local  illumina- 
tion. It  is  seen  by  contrast  with  the  adjacent  illuminated 
space ;  the  brighter  the  illumination  the  more  sensible  is 
the  difference.  Now,  the  beam  employed  in  the  foregoing 
experiments  is  not  of  the  same  brightness  throughout  its 
entire  transverse  section.  Pass  a  white  switch,  or  an  ivory 
paper-cutter,  rapidly  across  the  beam,  the  impression  of  its 
section  will  linger  on  the  retina.  The  section  seems  to  float 
for  a  moment  in  the  air  as  a  luminous  circle,  with  a  rim  much 
brighter  than  its  central  portion.  The  core  of  the  beam  is 
thus  seen  to  be  enclosed  by  an  intensely-luminous  sheath. 
An  effect  complementary  to  this  is  observed  when  the  beam 
is  intersected  by  the  dark  band  from  the  platinum  wire. 
The  brighter  the  illumination  the  greater  must  be  the  rela- 
tive darkness  consequent  on  the  withdrawal  of  the  light. 


DUST  AND  DISEASE.  285 

Hence  the  cross-section  of  the  sheath  surrounds  the  dark 
band  as  a  darker  ring. 

Oxygen,  hydrogen,  nitrogen,  carbonic  acid,  so  prepared 
as  to  exclude  all  floating  particles,  produce  the  darkness 
when  poured  or  blown  into  the  beam.  Coal-gas  does  the 
same.  An  ordinary  glass  shade  placed  in  the  air  with  its 
mouth  downward  permits  the  track  of  the  beam  to  be  seen 
crossing  it.  Let  coal-gas  or  hydrogen  enter  the  shade  by  a 
tube  reaching  to  its  top,  the  gas  gradually  fills  the  shade 
from  the  top  downward.  As  soon  as  it  occupies  the  space 
crossed  by  the  beam,  the  luminous  track  is  instantly  abol- 
ished. Lifting  the  shade  so  as  to  bring  the  common  bound- 
ary of  gas  and  air  above  the  beam,  the  track  flashes  forth. 
After  the  shade  is  full,  if  it  be  inverted,  the  gas  passes  up- 
ward like  a  black  smoke  among  the  illuminated  particles. 

The  air  of  our  London  rooms  is  loaded  with  this  organic 
dust,  nor  is  the  country  air  free  from  its  presence.  Howrever 
ordinary  daylight  may  permit  it  to  disguise  itself,  a  suffi- 
ciently powerful  beam  causes  dust  suspended  in  air  to  ap- 
pear almost  as  a  semi-solid.  Nobody  could,  in  the  first 
instance,  without  repugnance,  place  the  mouth  at  the  illu- 
minated focus  of  the  electric  beam  and  inhale  the  thickly- 
massed  dust  revealed  there.  Nor  is  the  repugnance  abol- 
ished by  the  reflection  that,  although  we  do  not  see  the 
floating  particles,  we  are  taking  them  into  our  lungs  every 
hour  and  minute  of  our  lives. 

The  Germ- Theory  of  Contagious  Disease. 

There  is  no  respite  to  this  contact  with  the  floating  mat- 
ter of  the  air  ;  and  the  wonder  is,  not  that  we  should  suffer 
occasionally  from  its  presence,  but  that  so  small  a  portion 
of  it,  and  even  that  but  rarely  diffused  over  large  areas, 
should  appear  to  be  deadly  to  man.  And  what  is  this  por- 
tion ?  It  was  some  time  ago  the  current  belief  that  epidemic 


286  FRAGMENTS  OF  SCIENCE. 

diseases  generally  were  propagated  by  a  kind  of  malaria, 
which  consisted  of  organic  matter  in  a  state  of  motor-decay; 
that  when  such  matter  was  taken  into  the  body  through 
the  lungs,  skin,  or  stomach,  it  had  the  power  of  spreading 
there  the  destroying  process  which  had  attacked  itself. 
Such  a  power  was  visibly  exerted  in  the  case  of  yeast.  A 
little  leaven  was  seen  to  leaven  the  whole  lump,  a  mere 
speck  of  matter  in  this  supposed  state  of  decomposition  be- 
ing apparently  competent  to  propagate  indefinitely  its  own 
decay.  Why  should  not  a  bit  of  rotten  malaria  work  in  a 
similar  manner  within  the  human  frame  ?  In  1836  a  very 
wonderful  reply  was  given  to  this  question.  In  that  year 
Cagniard  de  la  Tour  discovered  the  yeast-plant,  a  living  or- 
ganism, which,  when  placed  in  a  proper  medium,  feeds,  grows, 
and  reproduces  itself,  and  in  this  way  carries  on  the  process 
which  we  name  fermentation.  By  this  striking  discovery 
fermentation  was  connected  with  organic  growth. 

Schwann,  of  Berlin,  discovered  the  yeast-plant  inde- 
pendently about  the  same  time ;  and  in  February,  1837,  he 
also  announced  the  important  result  that,  when  a  decoction 
of  meat  is  effectually  screened  from  ordinary  air,  and  sup- 
plied solely  with  calcined  air,  putrefaction  never  sets  in. 
Putrefaction,  therefore,  he  affirmed  to  be  caused  by  some- 
thing derived  from  the  air,  which  something  could  be  de- 
stroyed by  a  sufficiently  high  temperature.  The  results  of 
Swann  were  confirmed  by  the  independent  experiments  of 
Helmholtz,  Ure,  and  Pasteur,  while  other  methods,  pursued 
by  Schultze  and  by  Schroeder  and  Dusch,  led  to  the  same 
result.  But  as  regards  fermentation,  the  minds  of  chemists, 
influenced  probably  by  the  great  authority  of  Gay-Lussac, 
fell  back  upon  the  old  notion  of  matter  in  a  state  of  decay. 
It  was  not  the  living  yeast-plant,  but  the  dead  or  dying 
parts  of  it,  which,  assailed  by  oxygen,  produced  the  fer- 
mentation. This  notion  was  finally  exploded  by  Pasteur. 
He  proved  that  the  so-called  "  ferments  "  are  not  such ; 


DUST  AND   DISEASE.  287 

that  the  true  ferments  are  organized  beings,  which  find  in 
the  reputed  ferments  their  necessary  food. 

Side  by  side  with  these  researches  and  discoveries,  and 
fortified  by  them  and  others,  has  run  the  germ-theory  of 
epidemic  disease.  The  notion  was  expressed  by  Kircher 
and  favored  by  Linnaeus,  that  epidemic  diseases  are  due 
to  germs  which  float  in  the  atmosphere,  enter  the  body,  and 
produce  disturbance  by  the  development  within  the  body 
of  parasitic  life.  While  it  was  still  struggling  against 
great  odds,  this  theory  found  an  expounder  and  a  defender 
in  the  President  of  this  institution.  At  a  time  when  most 
of  his  medical  brethren  considered  it  a  wild  dream,  Sir 
Henry  Holland  contended  that  some  form  of  the  germ- 
theory  was  probably  true.  The  strength  of  this  theory 
consists  in  the  perfect  parallelism  of  the  phenomena  of  con- 
tagious disease  with  those  of  life.  As  a  planted  acorn 
gives  birth  to  an  oak  competent  to  produce  a  whole  crop 
of  acorns,  each  gifted  with  the  power  of  reproducing  its 
parent-tree ;  and  as  thus  from  a  single  seedling  a  whole 
forest  may  spring ;  so,  it  is  contended,  these  epidemic  dis- 
eases literally  plant  their  seeds,  grow,  and  shake  abroad 
new  germs,  which,  meeting  in  the  human  body  their  proper 
food  and  temperature,  finally  take  possession  of  whole 
populations.  There  is  nothing  to  my  knowledge  in  pure 
chemistry  which  resembles  the  power  of  self-multiplication 
possessed  by  the  matter  which  produces  epidemic  disease. 
If  you  sow  wheat  you  do  not  get  barley  ;  if  you  sow  small- 
pox you  do  not  get  scarlet  fever,  but  small-pox  indefinitely 
multiplied,  and  nothing  else.  The  matter  of  each  con- 
tagious disease  reproduces  itself  as  rigidly  as  if  it  were  (as 
Miss  Nightingale  puts  it)  dog  or  cat. 

"arasitic  Diseases  of  SilJc-ivorms.     Pasteups  ResearcJies. 

It  is  admitted  on  all  hands  that  some  diseases  are  the 
product  of  parasitic  growth.  Both  in  man  and  lower  crea- 


288  FRAGMENTS  OF  SCIENCE. 

tures,  the  existence  of  such  diseases  has  been  demonstrated. 
I  am  enabled  to  lay  before  you  an  account  of  an  epidemic 
of  this  kind,  thoroughly  investigated  and  successfully  com- 
batted  by  M.  Pasteur.  For  fifteen  years  a  plague  had 
raged  among  the  silk-worms  of  France.  They  had  sickened 
and  died  in  multitudes,  while  those  that  succeeded  in  spin- 
ning their  cocoons  furnished  only  a  fraction  of  the  normal 
quantity  of  silk.  In  1853  the  silk  culture  of  France  pro- 
duced a  revenue  of  one  hundred  and  thirty  millions  of 
francs.  During  the  twenty  previous  years  the  revenue  had 
doubled  itself,  and  no  doubt  was  entertained  as  to  its  future 
augmentation.  The  weight  of  the  cocoons  produced  in 
1853  was  twenty-six  millions  of  kilogrammes ;  in  1865  it 
had  fallen  to  four  millions,  the  fall  entailing  in  the  single 
year  last  mentioned  a  loss  of  one  hundred  millions  of  francs. 
The  country  chiefly  smitten  by  this  calamity  happened 
to  be  that  of  the  celebrated  chemist,  Dumas,  now  perpetual 
secretary  of  the  French  Academy  of  Sciences.  He  turned 
to  his  friend,  colleague,  and  pupil,  Pasteur,  and  besought 
him  with  an  earnestness  which  the  circumstances  rendered 
almost  personal,  to  undertake  the  investigation  of  the 
malady.  Pasteur  at  this  time  had  never  seen  a  silk-worm, 
and  he  urged  his  inexperience  in  reply  to  his  friend.  But 
Dumas  knew  too  well  the  qualities  needed  for  such  an  in- 
quiry to  accept  Pasteur's  reason  for  declining  it.  "  Je 
mets,"  said  he,  "  un  prix  extreme  a'  voir  votre  attention 
fixee  sur  la  question  qui  interesse  mon  pauvre  pays;  la 
misere  surpasse  tout  ce  que  vous  pouvez  imaginer." 
Pamphlets  about  the  plague  had  been  showered  upon  the 
public,  the  monotony  of  waste-paper  being  broken  at  rare 
intervals  by  a  more  or  less  useful  publication.  "  The 
Pharmacopoeia  of  the  Silk-worm,"  wrote  M.  Cornalia  in 
1860,  "is  now  as  complicated  as  that  of  man.  Gases, 
liquids,  and  solids  have  been  laid  under  contribution. 
From  chlorine  to  sulphurous  acid,  from  nitric  acid  to  rum, 


DUST  AND   DISEASE.  289 

from  sugar  to  sulphate  of  quinine — all  has  been  invoked  in 
behalf  of  this  unhappy  insect."  The  helpless  cultivators, 
moreover,  welcomed  with  ready  trustfulness  every  new 
remedy,  if  only  pressed  upon  them  with  sufficient  hardi- 
hood. It  seemed  impossible  to  diminish  their  blind  confi- 
dence in  their  blind  guides.  In  1863  the  French  Minister 
of  Agriculture  himself  signed  an  agreement  to  pay  500,000 
francs  for  the  use  of  a  remedy  which  its  promoter  declared 
to  be  infallible.  It  was  tried  in  twelve  different  depart- 
ments of  France,  and  found  perfectly  useless.  In  no  single 
instance  was  it  successful.  It  was  under  these  circum- 
.stances  that  M.  Pasteur,  yielding  to  the  entreaties  of  his 
friend,  betook  himself  to  Alais  in  the  beginning  of  June, 
1865.  As  regards  silk  husbandry,  this  was  the  most  im- 
portant department  in  France,  and  it  was  also  that  which 
had  been  most  sorely  smitten  by  the  epidemic. 

The  silk-worm  had  been  previously  attacked  by  mus- 
cardine,  a  disease  proved  by  Bassi  to  be  caused  by  a  vege- 
table parasite.  Though  not  hereditary,  this  malady  was 
propagated  annually  by  the  parasitic  spores,  which,  wafted 
by  winds,  often  sowed  the  disease  in  places  far  removed 
from  the  centre  of  infection.  Muscardine  is  now  said  to 
be  very  rare ;  but  for  the  last  fifteen  or  twenty  years  a 
deadlier  malady  has  taken  its  place.  A  frequent  outward 
sign  of  this  new  disease  are  the  black  spots  which  cover 
the  silk-worms,  hence  the  name  pebrine,  first  applied  to 
the  plague  by  M.  de  Quatrefages,  and  adopted  by  Pasteur. 
Pebrine  declares  itself  in  the  stunted  and  unequal  growth 
of  the  worms,  in  the  languor  of  their  movements,  in  their 
fastidiousness  as  regards  food,  and  in  their  premature 
death.  The  track  of  discovery  as  regards  the  epidemic 
is  this:  In  1849  Guerin  M<§neville  noticed  in  the  blood 
of  silk-worms  vibratory  corpuscles  which  he  supposed  to 
be  endowed  with  independent  life.  Filippi  proved  him 
wrong,  and  showed  that  the  motion  of  the  corpuscles  was 
13 


290  FRAGMENTS  OF  SCIENCE. 

the  well-known  Brownian  motion.  But  Filippi  himself 
committed  the  error  of  supposing  the  corpuscles  ta  be 
normal  to  the  life  of  the  insect.  They  are  really  the  cause 
of  its  mortality — the  form  and  substance  of  its  disease. 
This  was  well  described  by  Cornalia ;  while  Lebert  and 
Frey  subsequently  found  the  corpuscles  not  only  in  the 
blood,  but  in  all  the  tissues  of  the  insect.  Osimo,  in  1857, 
discovered  them  in  the  eggs,  and  on  this  observation  Vitta- 
diani  founded,  in  1859,  a  practical  method  of  distinguishing 
healthy  from  diseased  eggs.  The  test  often  proved  falla- 
cious, and  it  was  never  extensively  applied. 

These  corpuscles  take  possession  of  the  intestinal  canal, 
and  spread  thence  throughout  the  body  of  the  worm. 
They  fill  the  silk  cavities,  the  stricken  insect  often  going 
through  the  motions  of  spinning  without  any  material  to 
answer  to  the  act.  Its  organs,  instead  of  being  filled  with 
the  clear  viscous  liquid  of  the  silk,  are  packed  to  disten- 
tion  by  the  corpuscles.  On  this  feature  of  the  plague  Pas- 
teur fixed  his  entire  attention.  The  cycle  of  the  silk- 
worm's life  is  briefly  this:  From  the  fertile  egg  comes 
the  little  worm,  which  grows,  and  casts  its  skin.  This  pro- 
cess of  moulting  is  repeated  two  or  three  times  at  subse- 
qjaent  intervals  during  the  life  of  the  insect.  After  the  last 
moulting  the  worm  climbs  the  brambles  placed  to  receive 
it,  and  spins  among  them  its  cocoon.  It  passes  thus  into 
a  chrysalis ;  the  chrysalis  becomes  a  moth,  and  the  moth 
when  liberated  lays  the  eggs  which  form  the  starting-point 
of  a  new  cycle.  Now  Pasteur  proved  that  the  plague-cor- 
puscles might  be  incipient  in  the  egg,  and  escape  detec- 
tion ;  they  might  also  be  germinal  in  the  worm,  and  still 
baffle  the  microscope.  But  as  the  worm  growrs,  the  cor- 
puscles grow  also,  becoming  larger  and  more  defined.  In 
the  aged  chrysalis  they  are  more  pronounced  than  in  the 
worm ;  while  in  the  moth,  if  either  the  egg  or  the  worm 
from  which  it  comes  should  have  been  at  all  stricken^  the 


DUST  AND  DISEASE.  291 

corpuscles  infallibly  appear,  offering  no  difficulty  of  detec- 
tion. This  was  the  first  great  point  made  out  in  1865  by 
Pasteur.  The  Italian  naturalists,  as  aforesaid,  recom- 
mended the  examination  of  the  eggs  before  risking  their 
incubation.  Pasteur  showed  that  both  eggs  and  worms 
might  be  smitten  and  still  pass  muster,  the  culture  of  such 
eggs  or  such  worms  being  sure  to  entail  disaster.  He  made 
the  moth  his  starting-point  in  seeking  to  regenerate  the  race. 
Pasteur  made  his  first  communication  on  this  subject  to 
the  Academy  of  Sciences  in  September,  1865.  It  raised 
a  cloud  of  criticism.  Here,  forsooth,  was  a  chemist  rashly 
quitting  his  proper  metier  and  presuming  to  lay  down  the  / 
law  for  the  physician  and  biologist  on  a  subject  which  was 
eminently  theirs.  "  On  trouva  etrange  que  je  fusse  si  peu 
au  courant  de  la  question  ;  on  m'opposa  des  travaux  qui 
avaient  paru  depuis  longtemps  en  Italie,  dont  les  r<§sultats 
montraient  Finutilit^  de  mes  efforts,  et  I'impossibilit6  d'ar- 
river  a  un  resultat  pratique  dans  la  direction  que  je  m'etais 
engage.  Que  mon  ignorance  fut  grande  au  sujet  des  re- 
cherches  sans  nombre  qui  avaient  paru  depuis  quinze  an- 
nees."  Pasteur  heard  the  buzz,  but  he  continued  his  work. 
In  choosing  the  eggs  intended  for  incubation,  the  cultiva- 
tors selected  those  produced  in  the  successful  "educa- 
tions "  of  the  year.  But  they  could  not  understand  the 
frequent  and  often  disastrous  failures  of  their  selected 
eggs ;  for  they  did  not  know,  and  nobody  prior  to  Pasteur 
was  competent  to  tell  them,  that  the  finest  cocoons  may 
envelope  doomed  corpusculous  moths.  It  was  not,  how- 
ever, easy  to  make  the  cultivators  accept  new  guidance. 
To  strike  their  imagination,  and  if  possible  determine  their 
practice,  Pasteur  hit  upon  the  expedient  of  prophecy.  In 
1866  he  inspected  at  St.  Hippolyte-du-Fort  fourteen  differ- 
ent parcels  of  eggs  intended  for  incubation.  Having  ex- 
amined a  sufficient  number  of  the  moths  which  produced 
these  eggs,  he  wrote  out  the  prediction  of  what  would  oc- 


292  FRAGMENTS  OF  SCIENCE. 

cur  in  1867,  and  placed  the  prophecy  as  a  sealed  letter  in 
the  hands  of  the  Mayor  of  St.  Hippolyte. 

In  1867  the  cultivators  communicated  to  the  mayor 
their  results.  The  letter  of  Pasteur  was  then  opened  and 
read,  and  it  was  found  that  in  twelve  out  of  fourteen  cases 
there  was  absolute  conformity  between  his  prediction  and 
the  observed  facts.  Many  of  the  groups  had  perished  to- 
tally ;  the  others  had  perished  almost  totally ;  and  this 
was  the  prediction  of  Pasteur.  In  two  out  of  the  fourteen 
cases,  instead  of  the  prophesied  destruction,  half  an  aver- 
age crop  was  obtained.  Now,  the  parcels  of  eggs  here  re- 
ferred to  were  considered  healthy  by  their  owners.  They 
had  been  hatched  and  tended  in  the  firm  hope  that  the  la- 
bor expended  on  them  would  prove  remunerative.  The  appli- 
cation of  the  moth-test  for  a  few  minutes  in  1866  would 
have  saved  the  labor  and  averted  the  disappointment.  Two 
additional  parcels  of  eggs  were  at  the  same  time  submitted 
to  Pasteur.  He  pronounced  them  healthy ;  and  his  words 
were  verified  by  the  production  of  an  excellent  crop. 
Other  cases  of  prophecy  still  more  remarkable,  because 
more  circumstantial,  are  recorded  in  Pasteur's  work. 

Pasteur  subjected  the  development  of  the  corpuscles  to 
a  searching  investigation.  "With  admirable  skill  and  com- 
pleteness he  examined  the  various  modes  by  which  the 
plague  is  propagated.  He  obtained  perfectly  healthy 
worms  from  moths  perfectly  free  from  corpuscles,  and  se- 
lecting from  them  10,  20,  30,  50,  as  the  case  might  be,  he 
introduced  into  the  worms  the  corpusculous  matter.  It  was 
first  permitted  to  accompany  the  food.  Let  us  take  a  sin- 
gle example  out  of  many.  Rubbing  up  a  small  corpuscu- 
lous worm  in  water,  he  smeared  the  mixture  over  the  mul- 
berry-leaves. Assuring  himself  that  the  leaves  had  been 
eaten,  he  watched  the  consequences  from  day  to  day.  Side 
by  side  with  the  infected  worms  he  reared  their  fellows, 
keeping  them  as  much  as  possible  out  of  the  way  of  infec- 


DUST  AND   DISEASE.  293 

tion.  These  constituted  his  "  lot  temoign,"  his  standard  of 
comparison.  On  the  16th  of  April,  1868,  he  thus  infected 
thirty  worms.  Up  to  the  23d  they  remained  quite  well. 
On  the  25th  they  seemed  well,  but  on  that  day  corpuscles 
were  found  in  the  intestines  of  two  of  them.  They  first 
form  in  the  tunic  of  the  intestine.  On  the  27th,  or  eleven 
days  after  the  infected  repast,  two  fresh  worms  were  exam- 
ined, and  not  only  was  the  intestinal  canal  found  in  each 
case  invaded,  but  the  silk-organ  itself  was  found  charged 
with  corpuscles.  On  the  28th,  the  twenty-six  remaining 
worms  were  covered  by  the  black  spots  of  pebrine.  On  the 
30th,  the  difference  of  size  between  the  infected  and  non- 
infected  worms  was  very  striking,  the  sick  worms  being  not 
more  than  two-thirds  of  the  size  of  the  healthy  ones.  On 
the  2d  of  May,  a  worm  which  had  just  finished  its  fourth 
moulting  was  examined.  Its  whole  body  was  so  filled  with 
corpuscles  as  to  excite  astonishment  that  it  could  live. 
The  disease  advanced,  the  worms  died  and  were  examined, 
and  on  the  llth  of  May  only  six  out  of  the  thirty  remained. 
They  were  the  strongest  of  the  lot,  but,  on  being  searched, 
they  also  were  found  charged  with  corpuscles.  Not  one  of 
the  thirty  worms  had  escaped ;  a  single  corpusculous  meal 
had  poisoned  them  all.  The  standard  lot,  on  the  contrary, 
spun  their  fine  cocoons,  and  two  only  of  their  moths  were 
found  to  contain  any  trace  of  corpuscles,  which  had,  doubt- 
less, been  introduced  during  the  rearing  of  the  worms. 

As  his  acquaintance  with  the  subject  increased,  Pas- 
teur's desire  for  precision  augmented,  and  he  finally  gives 
the  growing  number  of  corpuscles  seen  in  the  field  of  his 
microscope  from  day  to  day.  After  a  contagious  repast, 
the  number  of  worms  containing  the  parasite  gradually 
augmented  until  finally  it  became  cent,  per  cent.  The 
number  of  corpuscles  would  at  the  same  time  rise  from  0  to 
1,  to  10,  to  100,  and  sometimes  even  to  1,000  or  1,500  for  a 
single  field  of  his  microscope.  He  then  varied  the  mode 


294  FRAGMENTS  OF  SCIENCE. 

of  infection.  He  inoculated  healthy  worms  with  the  cor- 
pusculous  matter,  and  watched  the  consequent  growth  of 
the  disease.  He  showed  how  the  worms  inoculate  each 
other  by  the  infliction  of  visible  wounds  with  their  claws. 
In  various  cases  he  washed  the  claws,  and  found  corpuscles 
in  the  water.  He  demonstrated  the  spread  of  infection  by 
the  simple  association  of  healthy  and  diseased  worms.  The 
diseased  worms  sullied  the  leaves  by  their  dejections,  they 
also  used  their  claws,  and  spread  infection  -in  both  ways. 
It  was  no  hypothetical  infected  medium  that  killed  the 
worms,  but  a  definitely-organized  and  isolated  thing.  He 
examined  the  question  of  contagion  at  a  distance,  and  de- 
monstrated its  existence.  In  fact,  as  might  be  expected 
from  Pasteur's  antecedents,  the  investigation  was  exhaus- 
tive, the  skill  and  beauty  of  his  manipulation  finding  fitting 
correlatives  in  the  strength  and  clearness  of  his  thought. 

The  following  quotation  from  Pasteur's  work  clearly 
shows  the  relation  in  which  his  researches  stand  to  this 
great  question : 

"  Place,"  he  says,  "  the  most  skilful  educator,  even  the  most  expert 
rnicroscopist,  in  presence  of  large  educations  which  present  the  symp- 
toms described  in  our  experiments ;  his  judgment  will  necessarily  be  er- 
roneous if  he  confines  himself  to  the  knowledge  which  preceded  my  re- 
searches. The  worms  will  not  present  to  him  the  slightest  spot  of 
pcbrine  ;  the  microscope  will  not  reveal  the  existence  of  corpuscles  ;  the 
mortality  of  the  worms  will  be  null  or  insignificant ;  and  the  cocoons 
leave  nothing  to  be  desired.  Our  observer  would,  therefore,  conclude 
without  hesitation  that  the  eggs  produced  will  be  good  for  incubation. 
The  truth  is,  on  the  contrary,  that  all  the  worms  of  these  fine  crops  have 
been  poisoned  ;  that,  from  the  beginning,  they  carried  in  them  the  germ 
of  the  malady ;  ready  to  multiply  itself  beyond  measure  in  the  chrysa- 
lides and  the  moths,  thence  to  pass  into  the  eggs  and  smite  with  sterih'ty 
the  next  generation.  And  what  is  the  first  cause  of  the  evil  concealed 
under  so  deceitful  an  exterior  ?  In  our  experiments  we  can,  so  to  speak, 
touch  it  with  our  fingers.  It  is  entirely  the  effect  of  a  single  corpuscu- 
lous  repast ;  an  effect  more  or  less  prompt  according  to  the  epoch  of  life 
of  the  worm  that  has  eaten  the  poisoned  food." 


DUST  AND  DISEASE.  295 

Pasteur  describes  in  detail  his  method  of  securing 
healthy  eggs,  which  is  nothing  less  than  a  mode  of  restor- 
ing to  France  her  ancient  prosperity  in  silk  husbandry. 
And  the  justification  of  his  work  is  to  be  found  in  the  re- 
ports which  reached  him  of  the  application,  and  the  unpar- 
alleled success  of  his  method,  at  the  time  he  was  putting 
his  researches  together  for  final  publication.  In  France 
and  Italy  his  method  has  been  pursued  with  the  most  sur- 
prising results.  It  was  an  up-hill  fight  which  led  to  this 
triumph,  but  opposition  stimulated  Pasteur,  and  thus,  with- 
out meaning  it,  did  good  service.  "  Ever,"  he  says,  "  since 
the  commencement  of  these  researches,  I  have  been  ex* 
posed  to  the  most  obstinate  and  unjust  contradictions ;  but 
I  have  made  it  a  duty  to  leave  no  trace  of  these  contests  in 
this  book."  And,  in  reference  to  parasitic  diseases,  he  uses 
the  following  weighty  words :  "  II  est  au  pouvoir  de  1'homme 
de  faire  disparaitre  de  la  surface  du  globe  les  maladies  par- 
asitaires,  si,  comme  c'est  ma  conviction,  la  doctrine  des  gene"- 
rations  spontanees  est  une  chimere." 

Pasteur  dwells  upon  the  ease  with  which  an  island  like 
Corsica  might  be  absolutely  isolated  from  the  silk-worm 
epidemic.  And,  with  regard  to  other  epidemics,  Mr.  Simon 
describes  the  extraordinary  exemption  of  the  Scilly  Isles  for 
the  ten  years  extending  from  1851  to  1860.  Of  the  627 
registration  districts  of  England,  one  only  had  an  entire  es- 
cape from  diseases  which,  in  whole  or  in  part,  were  preva- 
lent in  all  the  others :  "  In  all  the  ten  years  it  had  not  a 
single  death  by  measles,  nor  a  single  death  by  small-pox, 
nor  a  single  death  by  scarlet  fever.  And  why  ?  Not  be- 
cause of  its  general  sanitary  merits,  for  it  had  an  average 
amount  of  other  evidence  of  unhealthiness.  Doubtless,  the 
reason  of  its  escape  was  that  it  was  insular.  It  was  the 
district  of  the  Scilly  Isles  •  to  which  it  was  most  improb- 
able that  any  febrile  contagion  should  come  from  without. 
And  its  escape  is  an  approximative  proof  that,  at  least  for 


296  FRAGMENTS  OF  SCIENCE. 

those  ten  years,  no  contagium  of  measles,  nor  any  contagium 
of  scarlet  fever,  nor  any  contagium  of  small-pox,  had  arisen 
spontaneously  within  its  limits."  It  may  be  added  that 
there  were  only  seven  districts  in  England  in  which  no 
death  from  diphtheria  occurred,  and  that,  of  those  seven  S 
districts,  the  district  of  the  Scilly  Isles  was  one.  s 

A  second  parasitic  disease  of  silk-worms,  called  in  France 
laflacherie,  coexistent  with  pebrine  but  quite  distinct  from 
it,  has  also  been  investigated.  Enough,  however,  has  been 
said  to  send  such  of  you  as  are  interested  in  these  questions 
to  the  original  volumes  for  further  information.  To  one 
important  practical  point  M.  Pasteur,  in  a  letter  written  to 
me,  directs  attention : 

"  Permettez-moi  de  terminer  ces  quelques  lignes  que  je  dois  dieter, 
vaincu  que  je  suis  par  la  maladie,  en  vous  faisant  observer  que  vous 
rendriez  service  aux  Colonies  de  la  Grande-Bretagne  en  repandant  la 
connaissance  de  ce  livre,  etdes  principes  que  j'etablistou  chant  la  maladie 
des  vers  a  soie.  Beaucoup  de  ces  colonies  pourraient  cultiver  le  murier 
avec  succes,  et  en  jetant  les  yeux  sur  mon  ouvrage  vous  vous  convaincrez 
aisement  qu'il  est  facile  aujourd'hui,  non-seulement  d'eloigner  la  maladie 
regnante,  mais  en  outre  de  donner  aux  recoltes  de  la  soie  une  prosperite 
qu'elles  n'ont  jamais  eue." 


Origin  and  Propagation  of  Contagious  Matter. 

Prior  to  Pasteur,  the  most  diverse  and  contradictory 
opinions  were  entertained  as  to  the  contagious  character  of 
pebrine ;  some  stoutly  affirmed  it,  others  as  stoutly  denied 
it.  But  on  one  point  all  were  agreed.  "  They  believed  in 
the  existence  of  a  deleterious  medium,  rendered  epidemic 
by  some  occult  and  mysterious  influence,  to  which  was  at- 
tributed the  cause  of  the  disease."  Those  acquainted  with 
medical  literature  will  not  fail  to  observe  an  instructive 
analogy  here.  We  have  on  the  one  side  accomplished 
writers  ascribing  epidemic  diseases  to  "  deleterious  media," 
which  arise  spontaneously  in  crowded  hospitals  and  over 


DUST  AND  DISEASE.  297 

ill-smelling  drains.  According  to  them  the  matter  of  epi- 
demic disease  is  formed  de  novo  in  a  putrescent  atmosphere. 
On  the  other  side  we  have  writers,  clear,  vigorous,  with 
well-defined  ideas  and  methods  of  research,  contending  that 
the  matter  which  produces  epidemic  disease  comes  always 
from  a  parent-stock.  It  behaves  as  germinal  matter,  and 
they  do  not  hesitate  to  regard  it  as  such.  They  no  more 
believe  in  the  spontaneous  generation  of  such  diseases  than 
they  do  in  the  spontaneous  generation  of  mice.  Pasteur, 
for  example,  found  that  pebrine  had  been  known  for  an  in- 
definite time  as  a  disease  among  silk-worms.  The  develop- 
ment of  it  which  he  combated  was  merely  the  expansion  of 
an  already  existing  power,  the  bursting  into  open  confla- 
gration of  a  previously  smouldering  fire.  There  is  nothing 
surprising  in  this ;  for  though  epidemic  disease  requires  a 
special  contagium  to  produce  it,  surrounding  conditions 
must  have  a  potent  influence  on  its  development.  Common 
seeds  may  be  duly  sown,  but  the  conditions  of  temperature 
and  moisture  may  be  such  as  to  restrict  or  altogether  pre- 
vent the  subsequent  growth.  Looked  at,  therefore,  from 
the  point  of  view  of  the  germ-theory,  the  exceptional  energy 
which  epidemic  disease  from  time  to  time  exhibits  is  not 
out  of  harmony  with  the  method  of  Nature.  You  some- 
times hear  diphtheria  spoken  of  as  if  it  were  a  new  disease 
of  the  last  twenty  years ;  but  Mr.  Simon  tells  me  that  from 
about  three  centuries  ago,  when  tremendous  epidemics  of  it 
began  to  rage  in  Spain  (where  it  was  named  Garrotitto), 
and  soon  afterward  in  Italy,  the  disease  has  been  well 
known  to  all  successive  generations  of  doctors ;  and  that, 
for  instance,  in  or  about  1758,  Dr.  Starr,  of  Liskeard,  in  a 
communication  to  the  Royal  Society,  particularly  described 
the  disease,  with  all  the  characters  which  have  recently 
again  become  familiar,  but  under  the  name  of  morbus  stran- 
gulatorius,  as  then  severely  epidemic  in  Cornwall ;  a  fact 
the  more  interesting  as  diphtheria,  in  its  more  modern  re- 


298  FRAGMENTS  OF  SCIENCE. 

appearance,  again  showed  predilection  for  that  remote 
county.  Many  also  believe  that  the  black  death  of  five 
centuries  ago.has  disappeared  as  mysteriously  as  it  came, 
but  Mr.  Simon  finds  that  it  is  believed  to  be  prevalent  at 
this  hour  in  some  of  the  northwestern  parts  of  India. 

Let  me  here  state  an  item  of  my  own  experience.  When 
I  was  at  the  Bel  Alp  last  year  the  clergyman  appointed  to 
that  station  received  letters  informing  him  of  the  breaking 
out  of  scarlet  fever  among  his  children.  He  lived,  if  I  re- 
member rightly,  on  the  healthful  eminence  of  Dartmoor, 
and  it  was  difficult  to  imagine  how  scarlet  fever  could  have 
been  wafted  to  the  place.  A  drain  ran  close  to  his  house, 
and  on  it  his  suspicions  were  manifestly  fixed.  Some  of 
our  medical  writers  would  fortify  him  in  this  notion,  while 
those  of  another  school  would  deny  to  a  drain,  however 
foul,  the  power  of  producing  a  specific  disease.  After  close 
inquiry,  he  recollected  that  a  hobby-horse  had  been  used 
both  by  his  boy  and  another  that  a  short  time  previously 
had  passed  through  scarlet  fever.  Drains  and  cesspools 
are  by  no  means  in  such  evil  odor  as  they  used  to  be.  A 
fetid  Thames  and  a  low  death-rate  occur  from  time  to  time 
together  in  London.  For,  if  the  special  matter  or  germs  of 
epidemic  disorder  be  not  present,  a  corrupt  atmosphere, 
however  obnoxious  otherwise,  will  not  produce  the  disorder. 
Corrupted  air  may  promote  an  epidemic,  but  cannot  origi- 
nate it.  On  the  other  hand,  through  the  transport  of  the 
special  germ  or  virus,  disease  may  develop  itself  in  regions 
where  the  drainage  is  good  and  the  atmosphere  pure. 

If  you  see  a  new  thistle  growing  in  your  field  you  feel 
sure  that  its  seed  has  been  wafted  thither.  Just  as  sure 
does  it  seem  that  the  contagious  matter  of  scarlatina,  or 
any  other  contagious  fever,  has  been  transplanted  to  the 
place  where  it  newly  appears.  With  a  clearness  and  con- 
clusiveness  not  to  be  surpassed  Dr.  William  Budd  has 
traced  such  diseases  from  place  to  place;  showing  how 


DUST  AND  DISEASE.  299 

they  plant  themselves  at  distinct  foci  among  populations 
subjected  to  the  same  atmospheric  influences,  just  as  grains 
of  corn  might  be  carried  in  the  pocket  and  sown.  Hilde- 
brand,  to  whose  remarkable  work,  Du  Typhus  Contagieux, 
Dr.  de  Mussy  has  directed  my  attention,  gives  the  following 
striking  case,  both  of  the  durability  and  the  transport  of 
the  virus  of  scarlatina :  "  Un  habit  noir  que  j'avais  en  visi- 
tant une  malade  attaque*e  de  scarlatine,  et  que  je  portai  de 
Vienne  de  Podolie,  sans  1' avoir  mis  depuis  plus  d'un  an  et 
demi,  me  communiqua,  des  que  je  fus  arrive,  cette  maladie 
contagieuse,  que  je  repandis  ensuite  dans  cette  province,  otl 
elle  etait  jusqu'alors  presque  inconnue."  Some  years  ago 
Dr.  de  Mussy  himself  was  summoned  to  a  country-house  in 
Surrey  to  see  a  young  lady  who  was  suffering  from  a  dropsy, 
evidently  the  consequence  of  scarlatina.  The  original  dis- 
ease being  of  a  very  mild  character  had  been  quite  over- 
looked, but  circumstances  were  recorded  which  could  leave 
no  doubt  upon  the  mind  as  to  the  nature  and  cause  of  the 
complaint.  But  then  the  question  arose,  how  did  the  young 
lady  catch  the  scarlatina  ?  She  had  come  there  on  a  visit 
two  months  previously,  and  it  was  only  after  she  had  been 
a  month  in  the  house  that  she  was  taken  ill.  The  house- 
keeper at  once  cleared  up  the  mystery.  The  young  lady 
on  her  arrival  had  expressed  a  particular  wish  to  occupy  a 
nice  room  in  an  isolated  tower,  and  in  that  room  six  months 
previously  a  visitor  had  been  confined  with  an  attack  of 
scarlatina.  The  room  had  been  swept  and  whitewashed, 
but  the  carpets  had  been  permitted  to  remain. 

Thousands  of  cases  could  probably  be  cited  in  which 
the  disease  has  shown  itself  in  this  mysterious  way,  but 
where  a  strict  examination  has  revealed  its  true  parentage 
and  extraction.  Is  it  then  philosophical  to  take  refuge  in 
the  fortuitous  concourse  of  atoms  as  a  cause  of  specific  dis- 
ease, merely  because  in  special  cases  the  parentage  may  be 
indistinct?  Those  best  acquainted  with  atomic  Nature, 


300  FRAGMENTS  OF  SCIENCE. 

and  who  are  most  ready  to  admit,  as  regards  even  higher 
things  than  this,  the  potentialities  of  matter,  will  be  the 
Jast  to  accept  these  rash  hypotheses. 

The  Germ-Theory  applied  to  Surgery. 

Not  only  medical  but  surgical  science  is  now  seeking 
light  and  guidance  from  this  germ-theory.  Upon  it  the 
antiseptic  system  of  Professor  Lister,  of  Edinburgh,  is 
founded ;  and  if  the  facts  be  correctly  given,  the  results 
are  extraordinary.  As  already  stated,  the  germ-theory  of 
putrefaction  was  started  by  Schwann,  but  the  illustrations 
of  this  theory  adduced  by  Professor  Lister  are  of  such,  pub- 
lic moment  as  not  only  to  justify,  but  to  render  imperative, 
their  introduction  here : 

Schwann's  observations,  says  Professor  Lister,  did  not  receive  the 
attention  which  they  appear  to  me  to  have  deserved.  The  fermentation 
of  sugar  was  generally  allowed  to  be  occasioned  by  the  torula  cerevisice  ; 
but  it  was  not  admitted  that  putrefaction  was  due  to  an  analogous 
agency.  And  yet  the  two  cases  present  a  very  striking  parallel.  In 
each  a  stable  chemical  compound,  sugar  in  the  one  case,  albumen  in  the 
other,  undergoes  extraordinary  chemical  changes  under  the  influence  of 
an  excessively  minute  quantity  of  a  substance  which,  regarded  chemi- 
cally, we  should  suppose  inert.  As  an  example  of  this  in  the  case  of 
putrefaction,  let  us  take  a  circumstance  often  witnessed  in  the  treatment 
of  large  chronic  abscesses.  In  order  to  guard  against  the  access  of  at- 
mospheric air,  we  used  to  draw  off  the  matter  by  means  of  a  canula  and 
trocar,  such  as  you  see  here,  consisting  of  a  silver  tube  with  a  sharp- 
pointed  steel  rod  fitted  into  it,  and  projecting  beyond  it.  The  instru- 
ment, dipped  in  oil,  was  thrust  into  the  cavity  of  the  abscess,  the  trocar 
was  withdrawn,  and  the  pus  flowed  out  through  the  canula,  care  being 
taken  by  gentle  pressure  over  the  part  to  prevent  the  possibility  of 
regurgitation.  The  canula  was  then  drawn  out  with  due  precaution 
against  the  reflux  of  air.  This  method  was  frequently  successful  as  to 
its  immediate  object,  the  patient  being  relieved  from  the  mass  of  the  ac- 
cumulated fluid,  and  experiencing  no  inconvenience  from  the  operation. 
But  the  pus  was  pretty  certain  to  reaccumulate  in  course  of  time,  and  it 
became  necessary  again  and  again  to  repeat  the  process.  And  unhappily 


DUST  AND   DISEASE.  301 

there  was  no  absolute  security  of  immunity  from  bad  consequences. 
However  carefully  the  procedure  was  conducted,  it  sometimes  happened, 
even  though  the  puncture  seemed  healing  by  first  intention,  that  feverish 
symptoms  declared  themselves  in  the  course  of  the  first  or  second  day, 
and,  on  inspecting  the  seat  of  the  abscess,  the  skin  was,  perhaps,  seen  to 
be  red,  implying  the  presence  of  some  cause  of  irritation,  while  a  rapid 
reaccumulation  of  the  fluid  was  found  to  have  occurred.  Under  these 
circumstances,  it  became  necessary  to  open  the  abscess  by  free  incision, 
when  a  quantity,  large  in  proportion  to  the  size  of  the  abscess,  say,  for 
example,  a  quart,  of  pus  escaped,  fetid  from  putrefaction.  Now,  how 
had  this  change  been  brought  about?  "Without  the  germ-theory,  I 
venture  to  say,  no  rational  explanation  of  it  could  have  been  given.  It 
must  have  been  caused  by  the  introduction  of  something  from  without. 
Inflammation  of  the  punctured  wound,  even  supposing  it  to  have  oc- 
curred, would  not  explain  the  phenomenon.  For  mere  inflammation, 
whether  acute  or  chronic,  though  it  occasions  the  formation  of  pus,  does 
not  induce  putrefaction.  The  pus  originally  evacuated  was  perfectly 
sweet,  and  we  know  of  nothing  to  account  for  the  alteration  in  its  quality 
but  the  influence  of  something  derived  from  the  external  world.  And 
what  could  that  something  be  ?  The  dipping  of  the  instrument  in  oil, 
and  the  subsequent  precautions,  prevented  the  entrance  of  oxygen.  Or 
even  if  you  allowed  that  a  few  atoms  of  the  gas  did  enter,  it  would  be 
an  extraordinary  assumption  to  make  that  these  could  in  so  short  a  time 
effect  such  changes  in  so  large  a  mass  of  albuminous  material.  Besides, 
the  pyogenic  membrane  is  abundantly  supplied  with  capillary  vessels, 
through  which  arterial  blood,  rich  in  oxygen,  is  perpetually  flowing; 
and  there  can  be  little  doubt  that  the  pus,  before  it  was  evacuated  at 
all,  was  liable  to  any  action  which  the  element  might  be  disposed  to 
exert  upon  it. 

On  the  oxygen-theory,  then,  the  occurrence  of  putrefaction  under 
these  circumstances  is  quite  inexplicable.  But  if  you  admit  the  germ- 
theory,  the  difficulty  vanishes  at  once.  The  canula  and  trocar  having 
been  lying  exposed  to  the  air,  dust  will  have  been  deposited  upon  them, 
and  will  be  present  in  the  angle  between  the  trocar  and  the  silver  tube, 
and  in  that  protected  situation  will  fail  to  be  wiped  off  when  the  instru- 
ment is  thrust  through  the  tissues.  Thus  when  the  trocar  is  withdrawn, 
some  portions  of  this  dust  will  naturally  remain  upon  the  margin  of  the 
canula,  which  is  left  projecting  into  the  abscess,  and  nothing  is  more 
likely  than  that  some  particles  may  fail  to  be  washed  off  by  the  stream 
of  out-flowing  pus,  but  may  be  dislodged  when  the  tube  is  taken  out, 
and  left  behind  in  the  cavity.  The  germ-theory  tells  us  that  these  par- 


302  FRAGMENTS  OF  SCIENCE. 

tides  of  dust  will  be  pretty  sure  to  contain  the  germs  of  putrefactive 
organisms,  and  if  one  such  is  left  in  the  albuminous  liquid,  it  will 
rapidly  develop  at  the  high  temperature  of  the  body,  and  account  for 
all  the  phenomena. 

But  striking  as  is  the  parallel  between  putrefaction  in  this  instance 
and  the  vinous  fermentation,  as  regards  the  greatness  of  the  effort  pro- 
duced, compared  with  the  minuteness  and  the  inertness,  chemically 
speaking,  of  the  cause,  you  will  naturally  desire  further  evidence  of  the 
similarity  of  the  two  processes.  You  can  see  with  the  microscope  the 
torula  of  fermenting  must  or  beer.  Is  there,  you  may  ask,  any  organism 
to  be  detected  in  the  putrefying  pus  ?  Yes,  gentlemen,  there  is.  If  any 
drop  of  the  putrid  matter  is  examined  with  a  good  glass,  it  is  found  to 
be  teeming  with  myriads  of  minute  jointed  bodies,  called  vibrios,  which 
indubitably  proclaim  their  vitality  by  the  energy  of  their  movements.  It 
is  not  an  affair  of  probability,  but  a  fact,  that  the  entire  mass  of  that 
quart  of  pus  has  become  peopled  with  living  organisms  as  the  result  of 
the  introduction  of  the  canula  and  trocar ;  for  the  matter  first  let  out 
was  as  free  from  vibrios  as  it  was  from  putrefaction.  If  this  be  so, 
the  greatness  of  the  chemical  changes  that  have  taken  place  in  the  pus 
ceases  to  be  surprising.  We  know  that  it  is  one  of  the  chief  peculiari- 
ties of  living  structures  that  they  possess  extraordinary  powers  of  effect- 
ing chemical  changes  in  materials  in  their  vicinity,  out  of  all  proportion 
to  their  energy  as  mere  chemical  compounds.  And  we  can  hardly  doubt 
that  the  animalcules  which  have  been  developed  in  the  albuminous  liquid, 
and  have  grown  at  its  expense,  must  have  altered  its  constitution,  just 
as  we  ourselves  alter  that  of  the  materials  on  "which  we  feed.1 

Secured  from  the  danger  of  putrefaction,  it  is  amazing 
how,  under  the  hands  of  a  really  able  surgeon,  the  human 
flesh  and  bones  may  be  cut,  torn,  and  crunched  with  im- 
punity. The  accounts  of  the  operations  of  our  eminent 
surgeons  read  like  romance.  On  this,  however,  I  must  not 
dwell  further  than  to  recommend  to  your  attention  a  case 
described  in  the  British  Medical  Journal  for  the  14th  of 
January  last.  In  the  operations  of  Professor  Lister  care 
is  taken  that  every  portion  of  tissue  laid  bare  by  the  knife 
shall  be  defended  from  germs ;  that  if  they  fall  upon  the 
wound  they  shall  be  killed  as  they  fall.  With  this  in  view 
1  Introductory  Lecture  before  the  University  of  Edinburgh. 


DUST  AND  DISEASE.  303 

he  showers  upon  his  exposed  surfaces  the  spray  of  diluted 
carbolic  acid,  which  is  particularly  deadly  to  the  germs, 
and  he  surrounds  the  wound  in  the  most  careful  manner 
with  antiseptic  bandages.  To  those  accustomed  to  strict 
experiment  it  is  manifest  that  we  have  a  strict  experimenter 
here— a  man  with  a  perfectly  distinct  object  in  view,  which 
he  pursues  with  never-tiring  patience  and  unwavering  faith. 
And  the  result,  in  his  hospital  practice,  as  described  by  him- 
self, has  been,  that  even  in  the  midst  of  abominations  too 
shocking  to  be  mentioned  here,  and  in  the  neighborhood 
of  wards  where  death  was  rampant  from  pyaemia,  erysipe- 
las, and  hospital  gangrene,  he  was  able  to  keep  his  patients 
absolutely  free  from  these  terrible  scourges.  Let  me  here 
recommend  to  your  attention  Professor  Lister's  "Intro- 
ductory Lecture  before  the  University  of  Edinburgh,"  which 
I  have  already  quoted ;  his  paper  on  "The  Effect  of  the 
Antiseptic  System  of  Treatment  on  the  Salubrity  of  a  Sur- 
gical Hospital ; "  and  the  article  in  the  British  Medical 
Journal,  to  which  I  have  just  referred. 

If,  instead  of  using  carbolic-acid  spray,  he  could  sur- 
round his  wounds  with  properly-filtered  air,  the  result 
would,  he  contends,  be  the  same.  In  a  room  where  the 
germs  not  only  float  but  cling  to  clothes  and  walls,  this 
would  be  difficult  if  not  impossible.  But  surgery  is  ac- 
quainted with  a  class  of  wounds  in  which  the  blood  is  freely 
mixed  with  air  that  has  passed  through  the  lungs,  and  it  is  a 
most  remarkable  fact  that  such  air  does  not  produce  putre- 
faction. Professor  Lister,  as  far  as  I  know,  was  the  first  to 
give  a  philosophical  interpretation  of  this  fact,  which  he 
decribes  and  comments  upon  thus : 

I  have  explained  to  my  own  mind  the  remarkable  fact  that  in  simple 
fracture  of  the  ribs,  if  the  lung  be  punctured  by  a  fragment,  the  blood 
effused  into  the  pleural  cavity,  though  freely  mixed  with  air,  undergoes 
no  decomposition.  The  air  is  sometimes  pumped  into  the  pleural  cavity 
in  such  abundance  that,  making  its  way  through  the  wound  in  the  pleura 


304  FRAGMENTS  OF  SCIENCE. 

cos  tails,  it  inflates  the  cellular  tissue  of  the  whole  body.  Yet  this  occa- 
sions no  alarm  to  the  surgeon  (although  if  the  blood  in  the  pleura  were  to 
putrefy,  it  would  infallibly  occasion  dangerous  suppurative  pleurisy). 
Why  air  introduced  into  the  pleural  cavity  through  a  wounded  lung 
should  have  such  wholly  different  effects  from  that  entering  directly 
through  a  wound  in  the  chest  was  to  me  a  complete  mystery  until  I  heard 
of  the  germ-theory  of  putrefaction,  when  it  at  once  occurred  to  me  that 
it  was  only  natural,  that  air  should  be  filtered  of  germs  by  the  air-pas- 
sages, one  of  whose  offices  is  to  arrest  inhaled  particles  of  dust,  and  pre- 
vent them  from  entering  the  air-cells. 

I  shall  have  occasion  to  refer  to  this  remarkable  hy- 
pothesis further  on. 

The  advocates  of  the  germ-theory,  both  of  putrefaction 
and  epidemic  disease,  hold  that  both  arise,  not  from  the  air, 
but  from  something  contained  in  the  air.  They  hold,  more- 
over, that  "  something  "  to  be  not  a  vapor  nor  a  foreign 
gas,  nor  indeed  a  molecule  of  any  kind,  but  a  particle? 
The  term  "  particulate  "  has  been  used  in  the  Reports  of 
the  Medical  Department  of  the  Privy  Council  to  describe 
this  supposed  constitution  of  contagious  matter ;  a,nd  Dr. 
Sanderson's  experiments  render  it  in  the  highest  degree 
probable,  if  they  do  not  actually  demonstrate,  that  the  virus 
of  small-pox  is  "  particulate."  Definite  knowledge  upon 
this  point  is  of  exceeding  importance,  because  in  the  treat- 
ment of  particles  methods  are  available  which  it  would  be 
futile  to  apply  to  molecules. 

Application  of  iMminous  Beams  to  researches  of  this 
nature. 

My  own  interference  with  this  great  question,  while 
sanctioned  by  eminent  names,  has  been  also  an  object  of 

1  As  regards  size,  there  is  probably  no  sharp  line  of  division  between 
molecules  and  particles ;  the  one  gradually  shades  into  the  other.  But 
the  distinction  that  I  would  draw  is  this :  the  atom  or  the  molecule,  if 
free,  is  always  part  of  a  gas,  the  particle  is  never  so.  A  particle  is  a  bit 
of  liquid  or  solid  matter  formed  by  the  aggregation  of  atoms  or  molecules. 


DUST  AND  DISEASE.  305 

varied  and  ingenious  attack.  On  this  point  I  will  only  say 
that  when  feeling  escapes  from  behind  the  intellect,  where 
it  is  a  useful  urging  force,  and  places  itself  in  front  of  the 
intellect,  it  is  liable  to  produce  glamour  and  all  manner 
of  delusions.  Thus  my  censors,  for  the  most  part,  have  lev- 
elled their  remarks  against  positions  which  I  never  assumed, 
and  against  claims  which  I  never  made.  The  simple  his- 
tory of  the  matter  is  this :  During  the  autumn  of  1868  I 
was  much  occupied  with  the  observations  referred  to  at  the 
beginning  of  this  discourse.  For  fifteen  years  I  had  ha- 
bitually employed  the  electric  light,  making  use  of  the 
floating  dust  to  reveal  the  paths  of  luminous  beams ;  but 
until  1868,  when  I  was  driven  to  it,  I  did  not  intentionally 
reverse  the  process  and  employ  a  luminous  beam  to  reveal 
and  examine  the  dust.  In  a  paper  presented  to  the  Royal 
Society  in  December,  1869, 1  thus  described  the  observa- 
tions which  induced  me  to  give  more  special  attention  to 
the  question  of  spontaneous  generation  and  the  germ- 
theory  of  epidemic  disease. 

The  Floating  Matter  of  the  Air. 

Prior  to  the  discovery  of  the  foregoing  action  (the  chemical  action  of 
light  upon  vapors),  and  also  during  the  experiments  just  referred  to,  the 
nature  of  my  work  compelled  me  to  aim  at  obtaining  experimental  tubes 
absolutely  clean  upon  the  surface,  and  absolutely  empty  within.  Neither 
condition  is,  however,  easily  attained. 

For  however  well  the  tubes  might  be  washed  and  polished,  and  how- 
ever bright  and  pure  they  might  appear  in  ordinary  daylight,  the  electric 
beam  infallibly  revealed  signs  and  tokens  of  dirt.  The  air  was  always 
present,  and  it  was  sure  to  deposit  some  impurity.  All  chemical  pro- 
cesses, not  conducted  in  a  vacuum,  are  open  to  this  disturbance.  When 
the  experimental  tube  was  exhausted  it  exhibited  no  trace  of  floating 
matter,  but  on  admitting  the  air  through  the  U-tubes  containing  caustic 
potash  and  sulphuric  acid,  a  dust-cone  more  or  less  distinct  was  always  re- 
vealed by  the  powerfully-condensed  electric  beam. 

The  floating  motes  resembled  minute  particles  of  liquid  which  had 


306  FRAGMENTS  OF  SCIENCE. 

been  carried  mechanically  into  the  experimental  tube.  Precautions  were 
therefore  taken  to  prevent  any  such  transfer.  They  produced  little  or  no 
mitigation.  I  did  not  imagine  at  the  time  that  the  dust  of  the  external 
air  could  find  such  free  pa'ssage  through  the  caustic  potash  and  the  sul- 
phuric-acid tubes.  But  the  motes  really  came  from  without.  They  also 
passed  with  freedom  through  a  variety  of  ethers  and  alcohols.  In  fact, 
it  requires  long-continued  action  on  the  part  of  an  acid  first  to  wet  the 
motes  and  afterward  to  destroy  them.  By  carefully  passing  the  air 
through  the  flame  of  a  spirit-lamp  or  through  a  platinum  tube  heated  to 
bright  redness,  the  floating  matter  was  sensibly  destroyed.  It  was  there- 
fore combustible,  in  other  words,  organic  matter.  I  tried  to  intercept  it 
by  a  large  respirator  of  cotton-wool.  Close  pressure  was  necessary  to 
render  the  wool  effective.  A  plug  of  the  wool  rammed  pretty  tightly  into 
the  tube  through  which  the  air  passed  was  finally  found  competent  to 
hold  back  the  motes.  They  appeared  from  time  to  time  afterward  and 
gave  me  much  trouble ;  but  they  were  invariably  traced  in  the  end  to 
some  defect  in  the  purifying  apparatus — to  some  crack  or  flaw  in  the 
sealing-wax  employed  to  render  the  tubes  air-tight.  Thus  through  proper 
caie,  but  not  without  a  great  deal  of  searching  out  of  disturbances,  the 
experimental  tube,  even  when  filled  vdth  pure  air  or  vapor,  contains 
nothing  competent  to  scatter  the  light.  The  space  within  it  has  the  as- 
pect of  an  absolute  vacuum. 

An  experimental  tube  in  this  condition  I  call  optically  empty. 

The  simple  apparatus  employed  in  these  experiments  will  be  at  once 
understood  by  reference  to  the  figure  on  page  307.  S  S'  is  the  glass  ex- 
perimental tube  which  has  varied  in  length  from  1  to  5  feet,  and  which  may 
be  from  2  to  3  inches  in  diameter.  From  the  end  S  the  pipe  p p'  passes  to 
an  air-pump.  Connected  with  the  other  end  S'  we  have  the  flask  F,  con- 
taining the  liquid  whose  vapor  is  to  be  examined  ;  then  follows  a  U-tube, 
T,  filled  with  fragments  of  clean  glass  wetted  with  sulphuric  acid ;  then 
a  second  U-tube,  T',  containing  fragments  of  marble  wetted  with  caustic 
potash ;  and  finally  a  narrow  straight  tube,  1 £',  containing  a  tolerably 
tightly-fitting  plug  of  cotton-wool.  To  save  the  air-pump  gauge  from  the 
attack  of  such  vapors  as  act  on  mercury,  as  also  to  facilitate  observa- 
tion, a  separate  barometer  tube  was  employed. 

Through  the  cork  which  stops  the  flask  F  two  glass  tubes,  a  and  5,  pass 
air-tight.  The  tube  a  ends  immediately  under  the  cork  ;  the  tube  b,  on 
the  contrary,  descends  to  the  bottom  of  the  flask  and  dips  into  the  liquid. 
The  end  of  the  tube  b  is  drawn  out  so  as  to  render  very  small  the  orifice 
through  which  the  air  escapes  into  the  liquid". 

The  experimental  tube  S  S'  being  exhausted,  a  cock  at  the  end  S'  is 


308  FRAGMENTS  OF  SCIENCE. 

carefully  turned  on.  The  air  passes  slowly  through  the  cotton-wool,  the 
caustic  potash,  and  the  sulphuric  acid  in  succession.  Thus  purified  it 
enters  the  flask  F  and  bubbles  through  the  liquid.  Charged  with  vapor 
it  finally  passes  into  the  experimental  tube,  where  it  is  submitted  to  ex- 
amination. The  electric  lamp  L  placed  at  the  end  of  the  experimental 
tube  furnished  the  necessary  beam. 

"Wanting  the  cotton-wool  the  floating  matter  of  the  air 
ran  the  gantlet  of  this  system.  The  fact  thus  forced  upon 
my  attention  had  a  bearing  too  obvious  to  be  overlooked. 
It  rendered  at  once  evident  to  the  senses  why  air  filtered 
through  cotton- wool  is  incompetent  to  generate  animalcular 
life.  The  air  is  rendered  by  this  treatment  optically  pure ; 
in  other  words,  freed  from  all  floating  matter,  germs  in- 
cluded. But  the  observations  also  revealed  the  great 
liability  to  error  in  experiments  of  this  nature.  They 
showed  that  without  an  amount  of  care  which  was  hardly 
to  be  expected  in  all  cases,  error  would  be  inevitable.  It 
was  especially  manifest  that  the  chemical  method  of 
Schultze  might  lead  to  the  'most  erroneous  consequences ; 
that  neither  acids  nor  alkalies  had  the  power  of  rapid 
destruction  which  they  had  been  supposed  to  possess.  In 
short,  the  employment  of  the  luminous  beam  rendered 
evident  the  cause  of  success  in  experiments  rigidly  con- 
ducted like  those  of  Pasteur ;  while  it  made  equally  evident 
the  certainty  of  failure  in  experiments  less  severely  and  less 
skilfully  carried  out. 

Dr.  Bennetts  Experiments. 

Take,  for  example,  the  well-conceived  experiments  of 
Dr.  Hughes  Bennett,  described  before  the  Royal  Society 
of  Surgeons  in  Edinburgh,  on  January  17,  1868. 1  Into 
flasks  containing  decoctions  of  liquorice-root,  hay,  or  tea, 
Dr.  Bennett,  by  an  ingenious  method,  forced  air.  The  air 
was  driven  through  two  U-tubes,  the  one  containing  a  so- 

1  British  Medical  Journal,  13,  pt.  ii.  1868. 


DUST  AND   DISEASE.  309 

lution  of  caustic  potash,  the  other  sulphuric  acid.  "  All  the 
bent  tubes,"  says  Dr.  Bennett,  "  were  filled  with  fragments 
of  pumice-stone  to  break  up  the  air,  so  as  to  prevent  the 
possibility  of  any  germs  passing  through  in  the  centre  of 
bubbles."  The  air  also  passed  through  a  Liebig's  bulb 
containing  sulphuric  acid,  and  also  through  a  bulb  contain- 
ing gun-cotton. 

It  was  only  natural  for  Dr.  Bennett  to  believe  that  his 
bent  tubes  entirely  cut  off  the  germs.  Previous  to  the 
observations  just  referred  to  I  also  believed  in  their  compe- 
tence to  do  this.  But  these  observations  destroy  any  such 
notion.  The  gun-cotton,  moreover,  will  fail  to  arrest  the 
whole  of  the  floating  matter  unless  it  is  tightly  packed, 
and  there  is  no  indication  in  Dr.  Bennett's  memoir  that  it 
was  so  packed.  On  the  whole,  I  should  infer  from  the 
mere  inspection  of  the  apparatus  the  very  results  which 
Dr.  Bennett  has  described — a  retardation  of  the  develop- 
ment of  life,  a  total  absence  of  it  in  some  cases,  and  its 
presence  in  others. 

In  his  first  series  of  experiments  eight  flasks  were  fed 
with  his  sifted  air,  and  five  with  common  air.  In  ten  or 
twelve  days  all  the  five  had  fungi  in  them;  while  it  re- 
quired from  four  to  nine  months  to  develop  fungi  in  the 
others.  In  one  case,  moreover,  even  after  this  interval,  no 
fungi  appeared.  In  a  second  series  of  experiments  there 
was  a  similar  exception.  In  a  third  series  of  experiments 
he  abandoned  the  cork  stoppers  used  in  the  first  and  second 
series,  and  employed  glass  stoppers.  Flasks  containing 
decoctions  of  tea,  beef,  and  hay,  were  filled  with  common 
air,  and  other  flasks  with  sifted  air.  In  every  one  of  the 
former  fungi  appeared,  and  in  not  one  of  the  latter.  These 
experiments  simply  ruin  the  doctrine  that  Dr.  Bennett 
finally  espouses. 

In  all  these  cases  the  prepared  air  was  forced  into  the 
infusion  when  it  was  boiling  hot.  Dr.  Bennett  made  a 


310  FRAGMENTS  OF  SCIENCE. 

fourth  series  of  experiments,  in  which,-  previous  to  forcing 
in  the  air,  he  permitted  the  flasks  to  cool.  Into  four  bottles 
thus  treated  he  forced  prepared  air,  and  after  a  time  found 
fungi  in  all  of  them.  What  is  his  conclusion  ?  Not  that 
the  boiling  hot  liquid  employed  in  his  first  experiments  had 
destroyed  such  germs  as  had  run  the  gantlet  of  his  ap- 
paratus ;  but  that  air  which,  previous  to  being  sealed  up, 
had  been  exposed  to  a  temperature  of  212°  is  too  rare  to 
support  life.  This  conclusion  is  so  remarkable  that  it  ought 
to  be  stated  in  Dr.  Bennett's  own  words :  "  It  may  be 
easily  conceived  that  air  subjected  to  a  boiling  temperature 
is  so  expanded  as  scarcely  to  merit  the  name  of  air,  and 
that  it  is  more  or  less  unfit  for  the  purpose  of  sustaining 
animal  or  vegetable  life," 

Now  numerical  data  are  attainable  here,  and,  as  a 
matter  of  fact,  I  live  and  flourish  for  a  considerable  portion 
of  each  year  in  air  of  less  density  than  that  which  Dr. 
Bennett  describes  as  scarcely  meriting  the  name  of  air; 
the  Swiss  men,  women,  children,  flocks,  herds,  tadpoles, 
grasshoppers,  flowers,  and  grasses,  do  the  same,  while  the 
chamois  rears  its  kids  in  air  rarer  still. 

In  a  fifth  series  of  experiments  sixteen  bottles  were 
filled  with  infusions.  Into  four  of  them,  while  cold,  or- 
dinary unheated  and  unsifted  air  was  pumped.  In  these 
four  bottles  fungi  were  developed.  Into  four  other  bottles, 
containing  a  boiling  infusion,  ordinary  air  was  also  pumped 
- — no  fungi  were  here  developed.  Into  four  other  bottles 
containing  an  effusion  which  had  been  boiled  and  permitted 
to  cool,  sifted  air  was  pumped — no  fungi  were  developed. 
Finally,  into  four  bottles  containing  a  boiling  infusion, 
sifted  air  was  pumped — no  fungi  were  developed.  Only, 
therefore,  in  the  four  cases  where  the  infusions  were  cold 
infusions,  and  the  air  ordinary  air,  did  fungi  appear. 

Dr.  Bennett  does  not  draw  from  these  experiments  the 
conclusion  to  which  they  so  obviously  point.  On  them,  on 


DUST  AND   DISEASE.  311 

the  contrary,  their  author  founds  a  defence  of  the  doctrine 
of  spontaneous  generation,  and  a  general  theory  of  sponta- 
neous development.  So  strongly  was  he  impressed  with 
the  idea  that  the  germs  could  not  possibly  pass  through  his 
potash  and  sulphuric-acid  tubes,  that  the  appearance  of 
fungi,  even  in  a  small  minority  of  cases,  where  the  air  had 
been  sent  through  these  tubes,  was  to  him  conclusive  evi- 
dence of  the  spontaneous  origin  of  such  fungi.  And  he 
accounts  for  the  absence  of  life  in  many  of  his  experi- 
ments by  resorting  to  an  hypothesis  which  will  not  bear 
a  moment's  consideration.  But  now  that  we  know  that 
organic  particles  may  pass  unscathed  through  alkalies  and 
acids,  the  experiments  of  Dr.  Bennett  are  precisely  what 
ought,  under  the  circumstances,  to  be  expected.  Indeed, 
their  harmony,  with  the  conditions  now  revealed,  is  a  proof 
of  the  honesty  and  accuracy  with  which  they  were  executed. 
On  another  point  also  the  luminous  beam  will  cast  a 
light.  Pasteur  opened  flasks  upon  the  Mer  de  Glace,  and, 
being  careful  not  to  come  between  the  wind  and  his  flasks, 
found  the  air  incompetent,  in  the  great  majority  of  cases, 
to  generate  life.  M.  Pouchet  repeated  Pasteur's  experiment 
in  the  Pyrenees,  adding  the  precaution  of  holding  the  flasks, 
when  they  were  opened,  above  his  head.  The  luminous 
beam  at  once  shows  us  the  effect  of  this  additional  precau- 
tion. Let  smoking  brown  paper  be  placed  at  the  open 
mouth  of  a  glass  shade  so  that  the  smoke  shall  ascend  and 
fill  the  shade.  A  beam  sent  through  the  shade  forms  a 
bright  track  through  the  smoke.  When  the  closed  fist  is 
placed  underneath  the  shade,  a  vertical  wind  of  surprising 
violence,  considering  the  small  elevation  of  temperature, 
rises  from  the  hand,  displacing  by  comparatively  dark  air 
the  illuminated  smoke.  Such  a  wind  infallibly  rose  from 
M.  Pouchet's  body  as  he  held  his  flasks  above  his  head,  and 
thus  the  precaution  of  Pasteur  of  not  coming  between  the 
wind  and  the  flask  was  annulled. 


312  FRAGMENTS  OF  SCIENCE. 

Again,  in  order  to  utterly  destroy  all  germs  M.  Pouchet 
produced  water  from  the  combustion  of  hydrogen  in  air ; 
but  even  in  this  water  he  found  organisms.  Had  he  seen, 
however,  as  you  have,  the  manner  in  which  the  air  is  clouded 
with  floating  matter,  would  he  have  concluded  that  the 
deportment  of  water  which  had  been  permitted  to  trickle 
through  such  air  could  have  the  least  influence  in  deciding 
this  great  question  ?  I  think  not.  Here  is  a  quantity  of 
water  produced  and  collected  by  allowing  a  hydrogen-flame 
to  play  upon  the  polished  bottom  of  a  silver  basin,  in  which 
ice  had  been  placed.  This  water  is  clear  in  the  common 
light ;  but  in  the  condensed  electric  beam  it  is  seen  to  be 
laden  with  particles,  so  thick-strewn  and  minute,  as  to  pro- 
duce a  continuous  cone  of  light.  In  passing  through  the 
air  the  water  loaded  itself  with  this  matter,  and  doubtless 
became  charged  with  incipient  life. 

Let  me  now  draw  your  attention  to  another  experiment 
of  Pasteur.  He  prepared  twenty-one  flasks,  each  contain- 
ing a  decoction  of  yeast,  filtered  and  clear.  He  boiled  the 
decoction,  so  as  to  destroy  whatever  germs  it  might  contain, 
and  while  the  space  above  the  liquid  was  filled  with  pure 
steam  he  sealed  his  flasks  with  a  blow-pipe.  He  opened  ten 
of  them  in  the  deep,  damp  caves  of  the  Paris  Observatory, 
and  eleven  of  them  in  the  court-yard  of  the  establishment. 
Of  the  former,  one  only  showed  signs  of  life  subsequently. 
In  nine  out  of  the  ten  flasks  no  organisms  of  any  kind 
were  developed.  In  all  the  others  organisms  speedily  ap- 
peared. 

Now  here  is  an  experiment  conducted  in  Paris ;  let  us 
see  whether  we  cannot  throw  light  upon  it  in  London.  I 
place  this  large  flask  in  the  beam,  and  you  see  the  luminous 
track  crossing  it  from  side  to  side.  The  flask  is  filled  with 
the  air  of  this  room,  charged  with  its  germs  and  its  dust, 
and  hence  capable  of  illumination.  But  here  is  another 
similar  flask,  which  cuts  a  clear  gap  out  of  the  beam.  It  is 


DUST  AND  DISEASE.  313 

filled  with  unfiltered  air,  and  still  no  trace  of  the  beam  is 
visible.  Why  ?  By  pure  accident  I  stumbled  on  this  flask 
in  our  apparatus-room,  where  it  had  remained  quiet  for 
some  time.  Here  are  three  other  flasks  which  have  also 
been  kept  quiet  for  a  couple  of  days  ;  they  are  all  optically 
empty.  The  still  air  of  the  flasks  has  deposited  its  dust, 
germs  and  all,  and  is  itself  practically  free  from  suspended 
matter.  Hence,  manifestly,  the  result  of  Pasteur. 

I  have  had  a  chamber  erected,  the  lower  half  of  which 
is  of  wood,  its  upper  half  being  enclosed  by  four  glazed 
window-frames.  The  chamber  tapers  to  a  truncated  cone 
at  the  top*  It  measures  in  plan  3  ft.  by  2  ft.  6  in.,  and  its 
height  is  5  ft.  10  in.  On  the  6th  of  February  this  chamber 
was  closed,  every  crevice  that  could  admit  dust,  or  cause 
displacement  of  the  air,  being  carefully  pasted  over  with 
paper.  The  electric  beam  at  first  revealed  the  dust  within 
the  chamber  as  it  did  in  the  air  of  the  laboratory.  The 
chamber  was  examined  almost  daily ;  a  perceptible  diminu- 
tion of  the  floating  matter  being  noticed  as  time  advanced. 
At  the  end  of  a  week  the  chamber  was  optically  empty, 
exhibiting  no  trace  of  matter  competent  to  scatter  the  light. 
But  where  the  beam  entered,  and  where  it  quitted  the 
chamber,  the  white  circles  stamped  upon  the  interior  sur- 
faces of  the  glass  showed  what  had  become  of  the  dust.  It 
clung  to  those  surfaces,  and  from  them  instead  of  from  the 
air,  the  light  was  scattered.  If  the  electric  beam  were  sent 
through  the  air  of  the  Paris  caves,  the  cause  of  its  impotence 
as  generator  of  life  would,  I  venture  to  predict,  be  revealed. 

These  experiments  illustrate  the  application  of  a  lumi- 
nous beam  to  researches  of  this  kind.  They  prove  that  the 
germs  which  produce  infusorial  and  fungoid  life  share  the 
fate  of  the  ordinary  visible  dust  with  which  they  are  inter- 
mixed ;  that  such  germs  attach  themselves  to  the  sides  of 
vessels,  and  fall  gradually  to  the  bottom  of  spaces  filled 
with  perfectly  still  air.  But  I  will  now  turn  to  a  far  more 
14 


314  FRAGMENTS  OF  SCIENCE. 

interesting  application  of  the  luminous  beam  than  any 
hitherto  described.  My  reference  to  Professor  Lister's 
interpretation  of  the  fact  that  air  which  has  passed  through 
the  lungs  cannot  produce  putrefaction  is  fresh  in  your  mem- 
ories. He  there  assumed  that  the  air  was  rendered  innocu- 
ous by  the  filtering  action  of  the  lungs.  Can  this  filtering 
process  be  taken  out  of  the  region  of  assumption  and  placed 
in  that  of  demonstration  ?  It  can. 

Here  is  the  concentrated  beam  with  which  we  operated 
at  the  commencement  of  this  discourse.  Its  track  through 
the  dust  is  luminous,  and  you  have  seen  the  blackness  in- 
troduced when  the  dust  is  burnt,  or  otherwise  removed.  I 
fill  my  lungs  with  ordinary  air  and  breathe  through  a  glass 
tube  across  the  beam.  The  condensation  of  the  aqueous 
vapor  of  the  breath  is  here  shown  by  the  formation  of  a 
luminous  white  cloud  of  delicate  texture.  It  is  necessary 
to  abolish  this  cloud,  and  this  may  be  done  by  drying  the 
breath  previous  to  its  entering  the  beam ;  or,  still  more 
simply,  by  warming  the  glass-tube.  When  this  is  done  the 
luminous  track  of  the  beam  is  for  a  time  uninterrupted, 
because  the  dust  returning  from  the  lungs  makes  good,  in 
great  part,  the  particles  displaced.  After  some  time,  how- 
ever, an  obscure  disk  appears  in  the  beam,  the  darkness  of 
which  increases,  until  finally,  toward  the  end  of  the  expira- 
tion, the  beam  is,  as  it  were,  pierced  by  an  intensely  black 
hole,  in  which  no  particles  whatever  can  be  discerned.  The 
deeper  air  of  the  lungs  is  absolutely  free  from  suspended 
matter.  It  is  therefore  in  the  precise  condition  required  by 
Professor  Lister's  explanation.  This  experiment  may* be 
repeated  any  number  of  times  with  the  same  result.  I  think 
it  must  be  regarded  as  a  crowning  piece  of  evidence  both 
of  the  correctness  of  Professor  Lister's  views  and  of  the 
impotence,  as  regards  vital  development,  of  optically  pure 
air, 


DUST  AND   DISEASE.  315 


Cotton-wool  ^Respirator. 

I  now  empty  my  lungs  as  perfectly  as  possible,  and 
placing  a  handful  of  cotton-wool  against  my  mouth  and 
nostrils,  inhale  through  it.  There  is  no  difficulty  in  thus 
filling  the  lungs  with  air.  On  expiring  this  air  through  a 
glass  tube,  its  freedom  from  floating  matter  is  at  once 
manifest.  From  the  very  beginning  of  the  act  of  expira- 
tion the  beam  is  pierced  by  a  black  aperture.  The  first 
puff  from  the  lungs  abolishes  the  illuminated  dust,  and  puts 
a  patch  of  darkness  in  its  place ;  and  the  darkness  con- 
tinues throughout  the  entire  course  of  the  expiration. 
When  the  tube  is  placed  below  the  beam  and  moved  to 
and  fro,  the  same  smoke-like  appearance  as  that  obtained 
with  a  flame  is  observed.  In  short,  the  cotton-wool,  when 
used  in  sufficient  quantity,  and  with  due  care,  completely 
intercepts  the  floating  matter  on  its  way  to  the  lungs.1 

The  application  of  these  experiments  is  obvious.  If  a 
physician  wishes  to  hold  back  from  the  lungs  of  his  patient, 
or  from  his  own,  the  germs  or  virus  by  which  contagious 
disease  is  propagated,  he  will  employ  a  cotton-wool  res- 
pirator. If  perfectly  filtered,  attendants  may  breathe  the 
air  unharmed.  In  all  probability  the  protection  of  the  lungs 
and  mouth  will  be  the  protection  of  the  entire  system.  For 
it  is  exceedingly  probable  that  the  germs  which  lodge  in 
the  air-passages,  or  find  their  way  with  the  saliva  into  the 
stomach  with  its  absorbent  system,  are  those  which  sow  in 

1  Since  the  first  publication  of  these  results,  Professor  Lister  has 
availed  himself  of  the  filtering  power  of  cotton-wool  in  the  treatment  of 
wounds.  He  first  destroys  the  germs  adhering  to  the  wool,  and  by  a 
proper  lotion  kills  those  that  may  be  scattered  on  the  flesh.  The  cleansed 
wool  placed  upon  the  wound  permits  of  a  free  diffusion  of  the  air,  but 
entirely  intercepts  the  germs,  and  thus  keeps  the  blood  perfectly  sweet. 
It  is  here  essential  that  no  matter  from  the  wound  should  reach  the  out- 
side air,  for  such  matter  would  open  a  highway  to  the  organisms. 


316  FKAGMENTS  OF  SCIENCE. 

the  body  epidemic  disease.  If  this  be  so,  then  disease  can 
be  warded  off  by  carefully-prepared  filters  of  cotton-wool. 
I  should  be  most  willing  to  test  their  efficacy  in  my  own 
person.  But  apart  from  all  doubtful  applications,  it  is  per- 
fectly certain  that  various  noxious  trades  in  England  may 
be  rendered  harmless  by  the  use  of  such  filters.  I  have 
had  conclusive  evidence  of  this  from  people  engaged  in 
such  trades.  A  form  of  respirator  devised  by  Mr.  Garrick, 
a  hotel  proprietor  in  Glasgow,  in  which  inhalation  and  ex- 
halation occur  through  two  different  valves,  the  one  per- 
mitting the  air  to  enter  through  the  cotton-wool,  and  the 
other  permitting  the  exit  of  the  air  direct  into  the  atmos- 
phere, is  well  adapted  for  this  purpose.  But  other  forms 
might  readily  be  devised. 

Fireman's  Respirator. 

Smoke  is  often  the  fireman's  greatest  obstacle  in  his 
efforts  to  save  life  ;  I  thought,  therefore,  of  inventing  a  res- 
pirator for  the  use  of  firemen.  Schroeder  was  the  first  to 
use  cotton-wool  as  a  filter.  To  catch  the  atmospheric 
germs,  M.  Pouchet  employed  a  film  of  adhesive  glycerine 
spread  upon  glass  ;  while  Dr.  Stenhouse  turned  charcoal  to 
important  account  in  respirators.  By  a  combination  of  all 
three  a  respirator  of  peculiar  efficacy  is  obtained.  For  the 
smoke  of  dried  leaves  the  cotton-wool  alone  was  found  an 
adequate  protection ;  but  for  the  far  more  pungent  smoke 
of  resinous  deal  it  was  found  totally  inadequate.  At  the 
suggestion  of  a  friend  I  moistened  the  wool  with  glycerine, 
and  found  it  a  great  improvement.  It  was  the  notion  of 
Pouchet  in  another  form.  Still  about  five  minutes  in  dense 
smoke  was  all  that  could  be  endured.  I  then  associated 
fragments  of  charcoal  with  the  moistened  cotton  ;  the  effect 
was  excellent.1  Armed  with  a  respirator  of  this  kind,  one 
1  Mr.  Ladd,  of  Beak  Street,  makes  these  respirators. 


DUST  AND  DISEASE.  317 

can  breathe  without  annoyance  in  a  space  so  crammed 
with  smoke,  that  a  single  inhalation  without  the  respirator 
would  be  intolerable.  I  wrote  to  the  chief  officer  of  the 
Metropolitan  Fire  Brigade,  asking  him  whether  such  a  res- 
pirator would  be  useful.  He  replied  to  me  that  it  would, 
but  added  that  he  was  aware  of  every  invention  of  the  kind 
in  all  the  countries  of  Europe,  and  that  none  had  been 
found  of  any  use.  At  my  invitation  he  was  kind  enough 
to  come  to  the  Royal  Institution  with  two  firemen  and  an 
assistant.  The  three  latter,  wearing  such  respirators,  went 
in  succession  into  the  smoke-filled  space,  and  on  returning, 
stated  that  they  had  not  experienced  the  slightest  discom- 
fort, that  they  could  have  remained  there  all  day  long. 
Captain  Shaw  himself  repeated  the  experiment  with  the 
same  result.  I  am  confident  that  sooner  or  later  this  res- 
pirator will  be  employed,  to  the  great  benefit  of  a  class  of 
men' whose  actions  in  critical  circumstances  I  have  often 
had  occasion  to  admire. 

Application  of  Luminous  Seams  to  Water. 

The  method  of  examination  here  pursued  is  also  appli- 
cable to  water.  It  is  in  some  sense  complementary  to  that 
of  the  microscope,  and  may  I  think  materially  aid  inquiries 
conducted  with  that  instrument.  In  microscopic  examina- 
tion attention  is  directed  to  a  small  portion  of  the  liquid, 
and  the  aim  is  to  detect  the  individual  suspended  particles. 
By  the  present  method  a  large  portion  of  the  liquid  is  il- 
luminated, its  general  condition  being  revealed,  through 
the  light  scattered  by  suspended  particles.  Care  is  taken 
to  defend  the  eye  from  the  access  of  all  other  light,  and, 
thus  defended,  it  becomes  an  organ  of  inconceivable  deli- 
cacy. Indeed,  an  amount  of  impurity  so  infinitesimal  as  to 
be  scarcely  expressible  in  numbers,  and  the  individual  par- 
ticles of  which  are  so  small  as  wholly  to  elude  the  micro- 


318  FRAGMENTS  OF  SCIENCE. 

scope,  may,  when  examined  by  the  method  alluded  to,  pro- 
duce not  only  sensible  but  striking  effects  upon  the  eye. 

I  take,  for  instance,  this  bottle  of  water  intended  to 
quench  your  lecturer's  thirst.  In  the  track  of  the  beam  it 
simply  reveals  itself  as  dirty  water.  So  you  see  that  we 
are  invaded  with  dirt  not  only  in  the  air  we  breathe,  but 
in  the  water  we  drink.  And  this  water  is  no  worse  than 
the  other  London  waters.  Thanks  to  the  kindness  of  Pro- 
fessor Frankland,  I  have  been  furnished  with  specimens  of 
the  water  of  eight  London  companies.  They  are  all  laden 
with  impurities  mechanically  suspended.  But  you  will  ask 
whether  filtering  will  not  remove  the  suspended  matter  ? 
The  grosser  matter,  undoubtedly,  but  not  the  more  finely- 
divided  matter.  Here  is  water  which  has  been  passed  four 
times  through  a  filter  of  bibulous  paper,  but  it  is  still  laden 
with  fine  matter.  Here,  also,  is  a  bottle  kindly  sent  me  by 
Mr.  Lipscomb,  and  passed  once  through  his  charcoal  filter. 
But  the  track  of  the  beam  through  it  is  more  luminous 
than  through  air,  because  the  quantity  of  matter  suspended 
in  the  wrater  is  greater  than  that  suspended  in  air.  Here 
is  another  specimen  courteously  sent  to  me  by  the  Silicated 
Carbon  Company.  All  the  grosser  matter  has  been  re- 
moved, but  it  is  thick  with  fine  matter.  Nine-tenths  of  the 
light  scattered  by  these  particles  is  perfectly  polarized  in  a 
direction  at  right  angles  to  the  beam,  and  this  release  of 
the  particles  from  the  ordinary  law  of  polarization  is  a 
demonstration  of  their  smallness.  I  should  say  by  far  the 
greater  number  of  the  particles  concerned  in  this  scattering 
are  wholly  beyond  the  range  of  the  microscope,  and  no  or- 
dinary filter  can  intercept  them.  There  is  an  aesthetic 
pleasure  in  the  drinking  of  a  glass  of  cold  sparkling  water, 
and  I  fear  these  experiments  will  destroy  this  pleasure  if 
you  ever  enjoyed  it.  And  it  is  next  to  impossible  by  arti- 
ficial means  to  produce  pure  water.  Mr.  Hartley,  for  ex- 
ample, some  time  ago  distilled  water  while  it  was  sur- 


DUST  AND  DISEASE.  319 

rounded  by  hydrogen,  but  the  water  was  not  free  from 
floating  matter.  It  is  so  hard  to  be  clean  in  the  midst  of 
dirt.  Here,  however,  is  an  approach  to  pure  water.  It  is 
from  the  Lake  of  Geneva,  and  the  bottle  was  carefully 
filled  for  me  by  my  distinguished  friend  Soret.  The  track 
of  the  beam  through  it  is  of  a  delicate  sky  blue ;  there  is 
scarcely  a  trace  of  grosser  matter. 

The  purest  water  that  I  have  seen — probably  the  purest 
which  has  been  seen  hitherto — has  been  obtained  from  the 
fusion  of  selected  specimens  of  ice.  But  extraordinary 
precautions  are  required  to  obtain  this  degree  of  purity. 
An  apparatus  was  devised  and  constructed  by  my  assistant 
for  this  purpose.  Through  the  plate  of  an  air-pump  passes 
the  shank  of  a  large  funnel,  attached  to  which  below  the 
plate  is  a  glass  bulb.  In  the  funnel  is  placed  a  block  of  the 
most  transparent  ice,  and  over  the  funnel  is  a  glass  receiver. 
This  is  first  exhausted  and  refilled  several  times  with  air, 
which  has  been  filtered  by  its  passage  through  cotton-wool, 
the  ice  being  thus  surrounded  by  pure  moteless  air.  But 
the  ice  has  previously  been  in  contact  with  mote-filled  air'; 
it  is,  therefore,  necessary  to  let  it  wash  its  own  face,  and 
wash  the  bulb  which  is  to  receive  the  water  of  liquefaction. 
The  ice  is  permitted  to  melt,  the  bulb  is  filled  and  emptied 
several  times,  until  finally  the  large  block  dwindles  to  a 
small  one.  We  may  be  sure  that  all  impurity  has  been 
thus  removed  from  the  surface  of  the  ice.  These  two  bulbs 
contain  water  obtained  in  this  way,  the  purity  of  which  is 
the  maximum  hitherto  attained.  Still  I  should  hesitate  to 
call  the  water  absolutely  pure.  When  the  concentrated 
beam  is  sent  through  it  the  track  of  the  beam  is  not  invis- 
ible, but  of  the  most  exquisitely  delicate  blue.  This  blue 
is  purer  than  that  of  the  sky,  so  that  the  matter  which  pro- 
duces it  must  be  finer  than  that  of  the  sky.  It  may  be, 
and  indeed  has  been,  contended  that  this  blue  is  scattered 
by  the  very  molecules  of  the  water,  and  not  by  matter  sus- 


320  FRAGMENTS  OF  SCIENCE. 

pended  in  it.  But  when  we  remember  that  this  perfection 
of  blue  is  approached  gradually  through  stages  of  less  per- 
fect blue;  and  when  we  consider  that  a  blue  in  all  re- 
spects similar  is  demonstrably  obtainable  from  particles 
mechanically  suspended,  we  should  hesitate,  I  think,  to 
conclude  that  we  have  arrived  here  at  the  last  stage  of  pu- 
rification. The  evidence,  I  think,  points  distinctly  to  the 
conclusion  that,  could  we  push  the  process  of  purification 
still  further,  even  this  last  delicate  trace  of  blue  would  dis- 
appear. 

Chalk  -  Water.     Clark's  /Softening  Process. 

But  is  it  not  possible  to  match  the  water  of  the  Lake 
of  Geneva  here  in  England  ?  Undoubtedly  it  is.  We  have 
in  England  a  kind  of  rock  which  constitutes  at  once  an  ex- 
ceedingly clean  recipient  and  a  natural  filter,  and  from  which 
we  can  obtain  water  extremely  free  from  mechanical  im- 
purities. I  refer  to  the  chalk-formation,  in  which  large 
quantities  of  water  are  held  in  store.  Our  chalk-hills  are 
in  most  cases  covered  with  thin  layers  of  soil,  and  with 
very  scanty  vegetation.  Neither  opposes  much  obstacle 
the  entry  of  the  rain  into  the  chalk,  where  any  organic 
impurity  which  the  water  may  carry  in  is  soon  oxidized 
and  rendered  harmless.  Those  who  have  scampered  like 
myself  over  the  downs  of  Hants  and  Wilts  will  remember 
the  scarcity  of  water  in  these  regions.  In  fact,  the  rain- 
fall, instead  of  washing  the  surface  and  collecting  in  streams, 
sinks  into  the  fissured  chalk  and  percolates  through  it,  and 
when  this  formation  is  suitably  tapped  we  obtain  water  of 
exceeding  briskness  and  purity.  Here  is  a  large  globe  filled 
with  the  water  of  a  well  near  Tring.  It  is  wonderfully  free 
from  mechanical  impurity ;  indeed,  it  stands  to  reason  that 
water  wholly  withdrawn  from  surface  contamination  and 
percolating  through  so  clean  a  substance  should  be  pure. 
Sending  a  beam  through  this  glass  of  water  its  purity  is 


DUST  AND   DISEASE.  321 

conspicuous ;  you  see  the  track  of  the  beam,  but  it  is  not 
the  thick  and  muddy  track  revealed  in  London  waters.  It 
has  been  a  subject  much  debated  whether  the  supply  of 
excellent  water  which  the  chalk  holds  in  store  could  not  be 
rendered  available  for  London.  Many  of  the  most  eminent 
engineers  and  chemists  have  ardently  recommended  this 
source,  and  have  sought  to  show  that  not  only  is  its 
purity  unrivalled,  but  that  its  quantity  is  practically  inex- 
haustible. Data  sufficient  to  test  this  are  now,  I  believe, 
in  existence ;  the  number  of  wells  sunk  in  the  chalk  is  so 
considerable  and  the  quantity  of  water  which  they  yield  is 
so  well  known. 

But  this  water,  so  admirable  as  regards  freedom  from 
mechanical  impurity,  labors  under  the  disadvantage  of 
being  very  hard.  It  is  rendered  hard  by  the  large  quantity 
of  carbonate  of  lime  which  it  holds  in  solution.  The  chalk- 
water  in  the  neighborhood  of  Watford  holds  in  solution 
about  seventeen  grains  of  carbonate  of  lime  per  gallon. 
This,  in  the  old  terminology,  used  to  be  called  seventeen 
degrees  of  hardness.  Now  this  hard  water  is  bad  for  tea, 
bad  for  washing  ;  it  furs  your  boilers,  because  the  lime 
held  in  solution  is  precipitated  by  boiling.  If  the  water  be 
used  cold,  its  hardness  must  be  neutralized  at  the  expense 
of  soap  before  it  will  give  a  lather.  These  are  serious  ob- 
jections to  the  use  of  chalk-water  in  London.  But  they 
are  now  successfully  met  by  the  experimental  demonstration 
that  such  water  can  be  softened  inexpensively,  and  on  a 
grand  scale.  I  had  long  known  the  method  of  softening 
water  called  Clark's  process,  but  not  until  recently,  under 
the  guidance  of  Mr.  Homersham,  did  I  see  proof  of  its 
larger  applications.  The  chalk-water  is  softened  for  the 
supply  of  the  city  of  Canterbury ;  at  the  Chiltern  Hills  it 
is  softened  for  the  supply  of  Tring  and  Aylesbury.  Carter- 
ham  also  enjoys  the  luxury. 

I  have  visited  all  these  places,  and  made  myself  ac- 


322  FRAGMENTS  OF  SCIENCE. 

quainted  with  the  works.  At  Canterbury  there  are  three 
reservoirs  covered  in  and  protected  by  a  concrete  roof  and 
layers  of  pebbles  both  from  the  summer's  heat  and  the  win- 
ter's cold.  Each  reservoir  contains  120,000  gallons  of  chalk- 
water.  Adjacent  to  these  reservoirs  are  others  containing 
pure  slacked  lime — the  so-called  "  cream  of  lime."  These 
are  filled  with  water,  the  lime  and  water  being  thoroughly 
mixed  by  air  forced  in  by  an  engine  through  apertures  in 
the  bottom  of  the  reservoir.  The  water  thus  well  mixed 
with  the  lime  soon  dissolves  all  of  this  substance  that  it  is 
capable  of  dissolving.  The  lime  is  then  allowed  to  subside 
to  the  bottom,  leaving  a  perfectly  clear  lime-water  behind. 
The  object  is  now  to  soften  the  chalk-water.  Into  the 
empty  reservoir  is  introduced  a  certain  quantity  of  the  clear 
lime-water,  and  after  this  about  nine  times  the  quantity  of  the 
chalk-water.  The  transparency  immediately  disappears — 
the  mixture  of  the  two  clear  liquids  becomes  thickly  turbid. 
The  carbonate  of  lime  is  precipitated,  and  the  precipitate  is 
permitted  to  subside  ;  it  is  crystalline  and  heavy,  and  there- 
fore sinks  rapidly.  In  about  twelve  hours  you  find  a  layer 
of  pure  white  carbonate  of  lime  at  the  bottom  of  the  reservoir, 
with  a  water  of  extraordinary  beauty  and  purity  overhead. 
A  few  days  ago  I  pitched  some  halfpence  into  a  reservoir 
sixteen  feet  deep  at  the  Chilton  Hills.  The  sixteen  feet 
hardly  perceptibly  dimmed  the  coin.  Had  I  cast  a  pin  in, 
it  could,  I  am  persuaded,  have  been  seen  at  the  bottom.  By 
this  process  of  softening  the  water  is  reduced  from  about 
seventeen  degrees  of  hardness  to  three  degrees  of  hardness. 
It  yields  a  lather  immediately.  Its  temperature  is  constant 
throughout  the  year.  In  the  hottest  summer  it  is  cool,  its 
temperature  being  20°  above  the  freezing-point;  and  it 
does  not  freeze  in  winter  if  conveyed  in  proper  pipes.  It 
is  not  exposed  to  the  contamination  of  either  earth  or  air. 
The  reservoirs  are  covered;  a  leaf  cannot  blow  into  the 
water,  no  surface  contamination  can  reach  it,  it  passes  di- 


DUST  AND  DISEASE.  323 

rect  from  the  main  into  the  house-tap ;  no  cisterns  are  em- 
ployed, the  supply  is  always  fresh  and  pure.  It  is  highly 
charged  with  air.  This  is  the  kind  of  water  which  is  sup- 
plied to  the  fortunate  people  of  Tring,  Caterham,  and  Can- 
terbury. 

Let  me,  in  conclusion,  remind  you  that  I  do  not  con- 
sider the  floating  matter  revealed  by  the  electric  beam  to  be 
all  living  matter.  I  believe  that  only  in  exceptional  cases, 
such  as  those  cited  in  the  excellent  reports  of  Dr.  Angus 
Smith,  does  the  quantity  of  living  matter  suspended  in  the 
air  of  our  streets  and  rooms  amount  to  more  than  a  small 
fraction  of  the  total  dust.  But  I  believe  it  to  be  perfectly 
well  established  that,  during  epidemics,  air  and  water  are 
charged  with  the  specific  "  materies  morbi  "  by  which  the 
disease  is  spread ;  that  these  two  media  are,  in  fact,  the 
chief  vehicles  of  its  dissemination.  I  believe  there  are  the 
strongest  grounds  for  holding  the  contagious  matter  to  be 
"  particulate,"  and  further,  that  the  particles  are  to  all  in- 
tents and  purposes  germs /  exhibiting  as  they  do  the  fun- 
damental characteristic  of  propagating  their  own  kind 
through  countless  generations,  and  over  vast  geographical 
areas.  Their  life  and  reproduction  run  parallel  to,  and  are 
an  incident  of  the  life  of  man  himself.  I  do  not  doubt  the 
ability  of  these  particles  to  scatter  light,  nor  that  the  means 
by  which  the  visible  floating  dust  of  our  air  is  arrested,  and 
which  demonstrably  arrest -with  it  the  germs  of  various 
forms  of  fungoid  and  animalcular  life,  including  those  con- 
cerned in  the  phenomena  of  putrefaction,  will  also  be  found 
effectual  in  arresting  contagium. 

The  following  extract  from  a  private  letter  written  to 
me  by  Dr.  William  Budd,  is  so  important,  and  its  reasoning 
is  so  cleaT,  that  I  asked  and  obtained  the  permission  of  its 
exceedingly  able  writer  to  publish  it : 

"  Another  point  of  great  practical  importance  is,  as  far 


324  FRAGMENTS  OF  SCIENCE. 

as  possible,  to  appraise  the  respective  shares  which  air  and 
water  take  in  the  great  act  of  distribution.  That  both 
cholera  and  typhoid  fever  are  sometimes  disseminated  by 
drinking-water  has  been  amply  proved.  I  have  myself  re- 
lated many  instances  of  the  fact,  and  have  in  my  notes  the 
record  of  many  others  still  more  striking.  But  that  water 
is  the  sole  or  even  the  chief  vehicle  of  cholera  and  typhoid 
is  a  notion  which,  if  I  may  trust  my  own  experience,  facts 
do  not  warrant. 

"  Limiting  myself,  for  the  moment,  to  the  case  of  typhoid, 
I  am  in  a  position  to  state  that  all  the  worst  and  most  wide- 
spread outbreaks  of  that  fever  which  I  have  ever  witnessed, 
have  occurred  among  communities  supplied  by  drinking- 
water  wilich  was  absolutely  blameless.  Two  illustrations 
will  suffice. 

"  I  live  in  a  town  in  which  the  divorce  between  sewage 
and  drinking-water  has  long  been  consummated.  Bristol 
is  supplied  with  drinking-water  which  from  its  source  in  the 
Mendips  to  the  tap  from  which  it  is  delivered  under  high 
pressure  to  the  consumer,  flows  through  conduits  out  of  all 
reach  of  sewage  contamination. 

"  And  yet  typhoid  fever  has  not  only  not  ceased  to  exist 
in  Bristol,  but  about  eight  or  ten  years  ago  (before  the 
appointment  of  a  health-officer),  there  occurred  in  the  Parish 
of  St.  James  one  of  the  worst  outbreaks  of  this  fever  which 
I  have  ever  seen  in  the  city.  .  In  the  course  of  a  circuit 
which  I  took  one  morning  with  the  late  Dr.  Pring  (at  that 
time  Poor  Law  Medical  Officer)  I  saw  within  a  compara- 
tively small  area  more  than  eighty  cases  of  the  disease. 

"  Now,  with  the  exception  of  a  single  household,  all  the 
patients  were  drinking  the  Mendip  water ;  the  very  same 
water  which,  as  far  as  fever  is  concerned,  more  than  150,000 
of  their  fellow-citizens  outside,  the  infected  area  were  drink- 
ing with  absolute  impunity. 

"  Some  four  or  five  years  ago  I  was  sent  for  to  advise 


DUST  AND  DISEASE.  325 

what  measures  should  be  taken  to  stay  an  outbreak  of 
typhoid  fever  which  had  occurred  in  a  large  convent  about 
two  miles  from  Bristol.  The  inmates  were  divided  into 
three  distinct  divisions  ;  the  largest  being  a  reformatory  for 
girls,  who  occupied  the  central  block  of  the  building.  Into 
this  reformatory  the  fever  was  brought  by  a  girl  already 
suffering  from  it,  and  who  had  contracted  it  in  a  sea-side 
place  more  than  twenty  miles  off.  From  this  girl  the  dis- 
ease spread  until,  at  the  date  of  my  visit,  more  than  fifty 
girls  were  lying  ill  of  it.  From  first  to  last  the  fever  was 
confined  to  the  reformatory  girls,  and  to  persons  in  immedi- 
ate attendance  upon  them. 

"  Now,  the  facts  as  to  the  drinking-water  were  these  : 

"  1.  The  water  was  proved  by  examination  of  the  well, 
and  by  chemical  analysis,  to  be  entirely  free  from  sewage 
contamination. 

"  2.  The  inmates  of  another  large  division  of  the  con- 
vent, who  remained  entirely  free  from  fever,  drank  the  same 
water  as  the  girls  among  whom  fever  was  raging  like  a 
plague. 

"  3.  From  the  very  time  when  disinfection  was  brought 
to  bear  on  the  excreta  the  disease  ceased  to  spread,  although 
the  inmates  of  the  infected  division  continued  to  drink  the 
same  water  as  before. 

"  Lastly,  nothing  has  since  been  done  to  the  well — the 
water  remains  what  it  was — but  no  fever  has  occurred  in 
the  convent  since. 

"  The  evidence  in  both  these  cases  is,  as  you  see,  of  that 
crucial,  decisive  order  that  admits  of  no  reply. 

"  They  show,  at  least,  that  typhoid  fever  may  do  its 
worst  where  drinking-water  takes  absolutely  no  part  in  the 
distribution  of  the  poison. 

"  But  if  water  be  excluded,  the  air  is  the  only  other 
possible  vehicle  by  which  a  poison  generated  in  the  living 
body  can  find  its  way  back  to  other  living  bodies  on  a  scale 


,126  FRAGMENTS  OF  SCIENCE. 

sufficiently  large  to  cause  the  resulting  disease  to  assume 
an  epidemic  form. 

"  I  may  remark  further  that  the  infection  of  the  air  in 
these  two  cases  was  obviously  not  the  work  of  chance,  but 
only  represented  the  effect  of  agencies  which  are  always  in 
operation  where  this  fever  prevails. 

"  The  phenomenon  is,  in  fact,  merely  the  expression  of  a 
general  law. 

"  The  germs  cast  off  in  the  liquid  excreta  of  contagious 
diseases  rise  into  the  air  by  no  power  of  their  own,  but  in 
virtue  of  the  very  same  physical  conditions  which  cause  the 
germs  of  the  great  tribe  of  Infusoria,  which,  as  their  name 
bespeaks,  breed  in  liquids,  to  rise  in  swarms  into  the  same 
medium. 

"  If  there  were  time  or  need,  I  could  show,  by  evidence 
quite  as  decisive,  that  all  these  statements  apply  equally  to 
cholera  also. 

"  I  do  not  know  that  there  is  any  thing  in  these  data  to 
suggest  additional  matter  for  your  essay,  but  I  have  thought 
it  worth  while  to  bring  them  under  your  notice,  harmoniz- 
ing as  they  do  with  your  own  investigations  which  show 
by  such  striking  phenomena  that  air  and  water  are  equally 
objects  of  distrust. 

"  As  to  the  germ-theory  itself,  that  is  a  matter  on  which 
I  have  long  since  made  up  my  mind.  From  the  day  when 
I  first  began  to  think  upon  these  subjects,  I  have  never  had 
a  doubt  that  the  specific  cause  of  contagious  fevers  must  be 
living  organisms. 

"  It  is  impossible,  in  fact,  to  make  any  statement  bearing 
upon  the  essence  or  distinctive  characters  of  these  fevers, 
without  using  terms  which  are  of  all  others  the  most  distinc- 
tive of  life.  Take  up  the  writings  of  the  most  violent  oppo- 
nent of  the  germ-theory,  and,  ten  to  one,  you  will  find  them 
full  of  such  terms  as  '  propagation,'  '  self-propagation,'  '  re- 
production,' 'self-multiplication,'  and  so  on.  Try  as  he 


DUST  AND  DISEASE.  327 

may — if  he  has  any  tiling  to  say  of  these  diseases  which  is 
characteristic  of  them — he  cannot  evade  the  use  of  these 
terms  or  the  exact  equivalents  of  them.  While  perfectly 
applicable  to  life  and  to  living  things,  these  terms  express 
qualities  which  are  not  only  inapplicable  to  common  chemi- 
cal agents,  but,  as  far  as  I  can  see,  actually  inconceivable 
of  them." 


XII. 
LIFE  AND  LETTERS  OF  FARADAY. 

BY  DR.   HENRY  BENCE  JONES. 


[The  Academy  for  May  and  June,  18TO.] 


Fame  is  the  spur  that  the  clear  spirit  doth  raise 
(That  last  infirmity  of  noble  minds) 
To  scorn  delights  and  live  laborious  days ; 
But  the  fair  guerdon  when  we  hope  to  find, 
And  think  to  burst  out  into  sudden  blaze, 
Comes  the  blind  fury  with  the  abhorred  shears, 
And  slits  the  thin-spun  life.     But  not  the  praise 
Phoebus  replied,  and  touched  my  trembling  ears  ; 
Fame  is  no  plant  that  grows  on  mortal  soil, 
Nor  in  the  glistering  foil 
Set  off  to  the  world,  nor  in  broad  rumor  lies, 
But  lives  and  spreads  aloft  by  those  pure  eyes 
And  perfect  witness  of  all-judging  Jove." 

SflLTOX. 


XII. 
LIFE  AND  LETTERS  OF  FARADAY. 

UNDERTAKEN  and  executed  in  a  reverent  and  loving 
spirit,  the  work  of  Dr.  Bence  Jones  makes  Faraday  the 
virtual  writer  of  his  own  life.  Everybody  now  knows  the 
story  of  the  philosopher's  birth;  that  his  father  was  a 
smith ;  that  he  was  born  at  Newington  Butts  in  1791 ; 
that  he  slid  along  the  London  pavements,  a  bright-eyed 
errand-boy,  with  a  load  of  brown  curls  upon  his  head  and  a 
packet  of  newspapers  under  his  arm ;  that  the  lad's  master 
was  a  bookseller  and  bookbinder  —  a  kindly  man,  who 
became  attached  to  the  little  fellow  and  in  due  time  made 
him  his  apprentice  without  fee ;  that  during  his  appren- 
ticeship he  found  his  appetite  for  knowledge  provoked  and 
strengthened  by  the  books  he  stitched  and  covered.  Thus 
he  grew  in  wisdom  and  stature  to  his  year  of  legal  man- 
hood, when  he  appears  in  the  volumes  before  us  as  a  writer 
of  letters,  which  reveal  his  occupation,  acquirements,  and 
tone  of  mind.  His  correspondent  was  Mr.  Abbott,  a  mem- 
ber of  the  Society  of  Friends,  who,  with  a  forecast  of  his 
friend's  greatness,  preserved  his  letters  and  produced  them 
at  the  proper  time. 

In  later  years  Faraday  always  carried  in  his  pocket  a 
blank  card  on  which  he  jotted  down  in  pencil  his  thoughts 
and  memoranda.  He  made  his  notes  in  the  laboratory, 
in  the  theatre,  and  in  the  streets.  This  distrust  of  his 
memory  reveals  itself  in  his  first  letter  to  Abbott.  To  a 


332  FKAGMENTS  OF  SCIENCE. 

proposition  that  no  new  inquiry  should  be  started  between 
them  before  the  old  one  had  been  exhaustively  discussed, 
Faraday  objects.  "  Your  notion,"  he  says,  "  I  can  hardly 
allow,  for  the  following  reason :  ideas  and  thoughts  spring 
up  in  my  mind  which  are  irrevocably  lost  for  want  of 
noting  at  the  time."  Gentle  as  he  seemed,  he  wished  to 
have  his  own  way,  and  he  had  it  throughout  his  life. 
Differences  of  opinion  sometimes  arose  between  the  two 
friends,  and  then  they  resolutely  faced  each  other.  "I 
accept  your  offer  to  fight  it  out  with  joy,  and  shall  in  the 
battle  of  experience  cause  not  pain,  but,  I  hope,  pleasure." 
Faraday  notes  his  own  impetuosity,  and  incessantly  checks 
it.  There  is  at  times  something  mechanical  in  his  self- 
restraint.  In  another  nature  it  would  have  hardened  into 
mere  "  correctness  "  of  conduct ;  but  his  overflowing  affec- 
tions prevented  this  in  his  case.  The  habit  became  a  second 
nature  to  him  at  last,  and  lent  serenity  to  his  later  years. 

In  October,  1812,  he  was  engaged  by  a  Mr.  De  la 
Roche  as  a  iourneyman  bookbinder ;  but  the  situation  did 
not  suit  him.  His  master  appears  to  have  been  an  austere 
and  passionate  man,  and  Faraday  was  to  the  last  degree 
sensitive.  All  his  life  he  continued  so.  He  suffered  at 
times  from  dejection  ;  and  a  certain  grimness,  too,  pervaded 
his  moods.  "  At  present,"  he  writes  to  Abbott,  "  I  am  as 
serious  as  you  can  be*  and  would  not  scruple  to  speak  a 
truth  to  any  human  being,  whatever  repugnance  it  might 
give  rise  to.  Being  in  this  state  of  mind,  I  should  have 
refrained  from  writing  to  you,  did  I  not  conceive  from  the 
general  tenor  of  your  letters  that  your  mind  is,  at  proper 
times,  occupied  upon  serious  subjects  to  the  exclusion  of 
those  that  are  frivolous."  Plainly  he  had  fallen  into  that 
stern  Puritan  mood  which  not  only  crucifies  the  flesh,  affec- 
tions, and  lusts  of  him  who  harbors  it,  but  is  often  a  cause 
of  disturbed  digestion  to  his  friends. 

About  three  months  after  his  engagement  with  De  la 


FARADAY.  333 

Roche,  Faraday  quitted  him  and  bookbinding  together. 
He  had  heard  Davy,  copied  his  lectures,  and  written  to  him 
entreating  to  be  released  from  trade,  which  he  hated,  and 
enabled  to  pursue  science.  Davy  recognized  the  merit  of 
his  correspondent,  kept  his  eye  upon  him,  and  when  oc- 
casion offered,  drove  to  his  door  and  sent  in  a  letter  offer- 
ing him  the  post  of  assistant  in  the  laboratory  of  the  Royal 
Institution.  He  was  engaged  upon  March  1,  1812,  and  on 
the  8th  we  find  him  extracting  the  sugar  from  beet-root. 
He  joined  the  City  Philosophical  Society  which  had  been 
founded  by  Mr.  Tatum  in  1808.  "The  discipline  was  very 
sturdy,  the  remarks  very  plain,  and  the  results  most  valu- 
able." Faraday  derived  great  profit  from  this  little  asso- 
ciation. In  the  laboratory  he  had  a  discipline  sturdier  still. 
Both  Davy  and  himself  were  at  this  time  cut  and  bruised 
by  explosions  of  chloride  of  nitrogen.  One  explosion  was 
so  rapid  "  as  to  blow  my  hand  open,  tear  away  a  part  of 
one  nail,  and  make  my  fingers  so  sore  that  I  cannot  use 
them  easily."  In  another  experiment  "  the  tube  and  re- 
ceiver were  blown  to  pieces ;  I  got  a  cut  on  the  head,  and 
Sir  Humphry  a  bruise  on  his  hand."  And  again,  speaking 
of  the  same  substance,  he  says :  "  When  put  in  the  pump 
and  exhausted,  it  stood  for  a  moment,  and  then  exploded 
with  a  fearful  noise.  Both  Sir  H.  and  I  had  masks  on,  but 
I  escaped  this  time  the  best.  Sir  H.  had  his  face  cut  in 
two  places  about  the  chin,  and  a  violent  blow  on  the  fore- 
head struck  through  a  considerable  thickness  of  silk  and 
leather."  It  was  this  same  substance  that  blew  out  the 
eye  of  Dulong. 

Over  and  over  again,  even  at  this  early  date,  we  can 
discern  the  quality  which,  compounded  with  his  rare  intel- 
lectual power,  made  him  a  great  experimental  philosopher. 
This  was  his  desire  to  see  facts,  and  not  to  rest  contented 
with  the  descriptions  of  them.  He  frequently  pits  the  eye 
against  the  ear,  and  affirms  the  enormous  superiority  of  the 


834  FRAGMENTS  OF  SCIENCE. 

organ  of  vision.  Late  in  life  I  have  heard  him  say  that  he 
could  never  have  fully  understand  an  experiment  until  he 
had  seen  it.  But  he  did  not  confine  himself  to  experiment. 
He  aspired  to  be  a  teacher,  and  reflected  and  wrote  upon 
the  method  of  scientific  exposition.  "  A  lecturer,"  he  ob- 
serves, "  should  appear  easy  and  collected,  undaunted  and 
unconcerned : "  still  "  his  whole  behavior  should  evince 
respect  for  his  audience."  These  recommendations  were 
afterward  in  great  part  embodied  by  himself.  I  doubt 
his  unconcern,  but  his  fearlessness  was  often  manifested. 
It  used  to  rise  within  him  as  a  wave,  which  carried  both 
him  and  his  audience  along  with  it.  On  rare  occasions 
also,  when  he  felt  himself  and  his  subject  hopelessly  unin- 
telligible, he  suddenly  evoked  a  certain  recklessness  of 
thought,  and  without  halting  to  extricate  his  bewildered 
followers,  he  would  dash  alone  through  the  jungle  into 
which  he  had  unwittingly  led  them  ;  thus  saving  them  from 
ennui  by  the  exhibition  of  a  vigor  which,  for  the  time  being, 
they  could  neither  share  nor  comprehend. 

In  October,  1813,  he  quitted  England  with  Sir  Hum- 
phry and  Lady  Davy.  During  his  absence  he  kept  a 
journal,  from  which  copious  and  interesting  extracts  have 
been  made  by  Dr.  Bence  Jones.  Davy  was  considerate, 
preferring  at  times  to  be  his  own  servant  rather  than 
impose  on  Faraday  duties  which  he  disliked.  But  Lady 
Davy  was  the  reverse.  She  treated  him  as  an  underling ; 
he  chafed  under  the  treatment,  and  was  often  on  the  point 
of  returning  home.  They  halted  at  Geneva.  De  la  Rive 
the  elder  had  known  Davy  in  1799,  and  by  his  writings  in 
the  "  Bibliotheque  Britannique,"  had  been  the  first  to  make 
the  English  chemist's  labors  known  abroad.  He  welcomed 
Davy  to  his  country  residence  in  1814.  Both  were  sports- 
men, and  they  often  went  out  shooting  together.  On  these 
occasions  Faraday  charged  Davy's  gun,  while  De  la  Rive 
charged  his  own.  Once  the  Genevese  philosopher  found 


FARADAY.  335 

himself  by  the  side  of  Faraday,  and  in  his  frank  and  genial 
way  entered  into  conversation  with  the  young  man.  It  was 
evident  that  a  person  possessing  such  a  charm  of  manner 
and  such  high  intelligence  could  be  no  mere  servant.  On 
inquiry  De  la  Rive  was  somewhat  shocked  to  find  that  the 
soi-disant  domestique  was  really  preparateur  in  the  labora- 
tory of  the  Royal  Institution :  and  he  immediately  proposed 
that  Faraday  thenceforth  should  join  the  masters  instead 
of  the  servants  at  their  meals.  To  this  Davy,  probably  out 
of  weak  deference  to  his  wife,  objected ;  but  an  arrangement 
was  come  to  that  Faraday  thenceforward  should  have  his 
food  in  his  own  room.  Rumor  states  that  a  dinner  in 
honor  of  Faraday  was  given  by  De  la  Rive.  This  is  a 
delusion  ;  there  was  no  such  banquet ;  but  Faraday  never 
forgot  the  kindness  of  the  friend  who  saw  his  merit  when 
he  was  a  mere  gar$on  de  laboratoire* 

He  returned  in  1815  to  the  Royal  Institution.  Here  he 
helped  Davy  for  years;  he  worked  also  for  himself,  and 
lectured  frequently  at  the  City  Philosophical  Society.  He 
took  lessons  in  elocution,  happily  without  damage  to  his 
natural  force,  earnestness,  and  grace  of  delivery.  He  was 
never  pledged  to  theory,  and  he  changed  in  opinion  as 
knowledge  advanced.  With  him  life  was  growth.  In  those 
early  lectures  we  hear  him  say,  "  In  knowledge,  that  man 
only  is  to  be  contemned  and  despised  who  is  not  in  a  state 
of  transition."  And  again,  "  Nothing  is  more  difficult  and 
requires  more  caution  than  philosophical  deduction,  nor  is 
there  any  thing  more  adverse  to  its  accuracy  than  fixity  of 
opinion."  Not  that  he  was  wafted  about  by  every  wind  of 

1  While  confined  last  autumn  at  Geneva  by  'the  effects  of  a  fall  in  the 
Alps,  my  friends,  with  a  kindness  I  can  never  forget,  did  all  that  friend- 
ship could  suggest  to  render  my  captivity  pleasant  to  me.  M.  de  la  Rive 
then  wrote  out  for  me  the  full  account,  of  which  the  foregoing  is  a  con- 
densed  abstract.  It  was  at  the  desire  of  Dr.  Bence  Jones  that  I  asked 
him  to  do  so.  The  rumor  of  a  banquet  at  Geneva  illustrates  the  ten 
dency  to  substitute  for  the  youth  of  1814  the  Faraday  of  later  years. 


336  FRAGMENTS  OF  SCIENCE. 

doctrine ;  but  that  he  united  flexibility  with  his  strength. 
In  striking  contrast  with  this  intellectual  expansiveness  is 
his  fixity  in  religion,  but  this  is  a  subject  which  cannot  be 
discussed  here. 

Of  all  the  letters  published  in  these  volumes  none 
possess  a  greater  charm  than  those  of  Faraday  to  his  wife. 
Here,  as  Dr.  Bence  Jones  truly  remarks,  "  he  laid  open  all 
his  mind  and  the  whole  of  his  character,  and  what  can  be 
made  known  can  scarcely  fail  to  charm  every  one  by  its 
loveliness,  its  truthfulness,  arid  its  earnestness."  Abbott 
and  he  sometimes  swerved  into  word-play  about  love ;  but 
up  to  1820,  or  thereabouts,  the  passion  was  potential 
merely.  Faraday's  journal,  indeed,  contains  entries  which 
show  that  he  took  pleasure  in  the  assertion  of  his  contempt 
for  love ;  but  these  very  entries  became  links  in  his  destiny. 
It  was  through  them  that  he  became  acquainted  with  one 
who  inspired  him  with  a  feeling  which  only  ended  with  his 
life.  His  biographer  has  given  us  the  means  of  tracing  the 
varying  moods  which  preceded  his  acceptance.  They  reveal 
more  than  the  common  alternations  of  light  and  gloom ;  at 
one  moment  he  wishes  that  his  flesh  might  melt  and  he 
become  nothing ;  at  another  he  is  intoxicated  with  hope. 
The  impetuosity  of  his  character  was  then  unchastened  by 
the  discipline  to  which  it  was  subjected  in  after-years.  The 
very  strength  of  his  passion  proved  for  a  time  a  bar  to  its 
advance,  suggesting  as  it  did  to  the  conscientious  mind  of 
Miss  Barnard  doubts  of  her  capability  to  return  it  with 
adequate  force.  But  they  met  again  and  again,  and  at 
each  successive  meeting  he  found  his  heaven  clearer,  until 
at  length  he  was  able  to  say, "  Not  a  moment's  alloy  of  this 
evening's  happiness  occurred.  Every  thing  was  delightful 
to  the  last  moment  of  my  stay  with  my  companion,  because 
she  was  so."  The  turbulence  of  doubt  subsided,  and  a  calm 
and  elevating  confidence  took  its  place.  "  What  can  I  call 
nyself,"  he  writes  to  her  in  a  subsequent  letter,  "  to  convey 


FARADAY.  337 

most  perfectly  my  affection  and  love  for  you  ?  Can  I  or 
can  truth  say  more  than  that  for  this  world  I  am  yours  ?  " 
Assuredly  he  made  his  profession  good,  and  no  fairer  light 
falls  upon  his  character  than  that  which  reveals  his  relations 
to  his  wife.  Never,  I  believe,  existed  a  manlier,  purer, 
steadier  love.  Like  a  burning  diamond  it  continued  to  shed 
for  six-and-forty  years  its  white  and  smokeless  glow. 

Faraday  was  married  on  June  12,  1821 ;  and  up  to  this 
date  Davy  appears  throughout  as  his  friend.  Soon  after- 
ward, however,  disunion  occurred  between  them,  which, 
while  it  lasted,  must  have  given  Faraday  intense  pain.  It 
is  impossible  to  doubt  the  honesty  of  conviction  with  which 
this  subject  has  been  treated  by  Dr.  Bence  Jones,  and  there 
may  be  facts  known  to  him,  but  not  appearing  in  these 
volumes,  which  justify  his  opinion  that  Davy  in  those  days 
had  become  jealous  of  Faraday.  This,  which  is  the  preva- 
lent belief,  is  also  reproduced  in  an  excellent  article  in 
the  March  number  of  Eraser's  Magazine.  But  the  best 
analysis  I  can  make  of  the  data  fails  to  present  Davy  in 
this  light  to  me.  The  facts,  as  I  regard  them,  are  briefly 
these : 

In  1820,  Oersted,  of  Copenhagen,  made  the  celebrated 
discovery  which  connects  electricity  with  magnetism,  and 
immediately  afterward  the  acute  mind  of  Wollaston  per- 
ceived that  a  wire  carrying  a  current  ought  to  rotate 
round  it  own  axis  under  the  influence  of  a  magnetic  pole. 
In  1821  he  tried,  but  failed,  to  realize  this  result  in  the 
laboratory  of  the  Royal  Institution.  Faraday  was  not  pres- 
ent at  the  moment,  but  he  came  in  immediately  afterward, 
and  heard  the  conversation  of  Wollaston  and  Davy  about 
the  experiment.  He  had  also  heard  a  rumor  of  a  wager 
that  Dr.  Wollaston  would  eventually  succeed. 

This  was  in  April.  In  the  autumn  of  the  same  year 
Faraday  wrote  a  history  of  electro-magnetism,  and  repeated 
for  himself  the  experiments  which  he  described.  It  was 
15 


338  FRAGMENTS  OF  SCIENCE. 

while  thus  instructing  himself  that  he  succeeded  in  causing 
a  wire  carrying  an  electric  current  to  rotate  round  a  mag- 
netic pole.  This  was  not  the  result  sought  by  Wollaston, 
but  it  was  closely  related  to  it. 

The  strong  tendency  of  Faraday's  mind  to  look  upon 
the  reciprocal  actions  of  natural  forces  gave  birth  to  his 
greatest  discoveries ;  and  we,  who  know  this,  should  be 
justified  in  concluding  that,  even  had  Wollaston  not  pre- 
ceded him,  the  result  would  have  been  the  same.  But  in 
judging  Davy  we  ought  to  transport  ourselves  to  his  time, 
and  carefully  exclude  from  our  thoughts  and  feelings  that 
noble  subsequent  life  which  would  render  simply  impossible 
the  ascription  to  Faraday  of  anything  unfair.  It  would  be 
unjust  to  Davy  to  put  our  knowledge  in  the  place  of  his, 
or  to  credit  him  with  data  which  he  could  not  have  pos- 
sessed. Rumor  and  fact  had  connected  the  name  of  Wol- 
laston with  these  supposed  interactions  between  magnets 
and  currents.  When,  therefore,  Faraday  in  October  pub- 
lished his  successful  experiment  without  any  allusion  to 
Wollaston,  general,  though  really  ungrounded,  criticism 
followed.  I  say  ungrounded  because,  firstly,  Faraday's  ex- 
periment was  not  that  of  Wollaston,  and  secondly,  Faraday, 
before  he  published  it,  had  actually  called  upon  Wollaston, 
and  not  finding  him  at  home  did  not  feel  himself  authorized 
to  mention  his  name. 

In  December  Faraday  published  a  second  paper  on  the 
same  subject,  from  which,  through  a  misapprehension,  the 
name  of  Wollaston  was  also  omitted.  Warburton  and 
others  thereupon  affirmed  that  Wollaston's  ideas  had  been 
appropriated  without  acknowledgment,  and  it  is  plain  that 
Wollaston  himself,  though  cautious  in  his  utterance,  was 
also  hurt*  Censure  grew  till  it  became  intolerable.  "I 
hear,"  writes  Faraday  to.  his  friend  Stodart,  "  every  day 
more  and  more  of  these  sounds,  which,  though  only  whis- 
pers, to  me,  arc,  I  suspect,  spoken  aloud  among  scientific 


FARADAY.  339 

men."  He  might  have  written  explanations  and  defences, 
but  he  went  straighter  to  the  point.  He  wished  to  see  the 
principals  face  to  face — to  plead  his  cause  before  them  per- 
sonally. There  is  a  certain  vehemence  in  his  desire  to  do 
this.  He  saw  Wollaston,  he  saw  Davy,  he  saw  Warbur- 
ton  ;  and  I  am  inclined  to  think  that  it  was  the  irresistible 
candor  and  truth  of  character  which  these  viva  voce  de- 
fences revealed,  as  much  as  the  defences  themselves,  that 
disarmed  resentment  at  the  time. 

As  regards  Davy,  another  cause  of  dissension  arose  in 
1823.  In  the  spring  of  that  year  Faraday  analyzed  the 
hydrate  of  chlorine,  a  substance  once  believed  to  be  the 
element  chlorine,  but  .proved  by  Davy  to  be  a  compound  of 
that  element  and  water.  The  analysis  was  looked  over  b}' 
Davy,  who  then  and  there  suggested  to  Faraday  to  heat 
the  hydrate  in  a  closed  glass  tube.  This  was  done,  the 
substance  was  decomposed,  and  one  of  the  products  of  de- 
composition was  proved  by  Faraday  to  be  chlorine  liquefied 
by  its  own  pressure.  On  the  day  of  its  discovery  he  com- 
municated this  result  to  Dr.  Paris.  Davy,  on  being  in- 
formed of  it,  instantly  liquefied  another  gas  in  the  same 
way.  Having  struck  thus  into  Faraday's  inquiry,  ought  he 
not  to  have  left  the  matter  in  Faraday's  hands  ?  I  think 
he  ought.  But,  considering  his  relation  to  both  Faraday 
and  the  hydrate  of  chlorine,  Davy,  I  submit,  may  be  excused 
for  thinking  differently.  A  father  is  not  always  wise  enough 
to  see  that  his  son  has  ceased  to  be  a  boy,  and  estrange- 
ment on  this  account  is  not  rare  ;  nor  was  Davy  wise  enough 
to  discern  that  Faraday  had  passed  the  mere  assistant 
stage  and  become  a  discoverer.  It  is  now  hard  to  avoid 
magnifying  this  error.  But  had  Faraday  died  or  ceased  to 
work  at  this  time,  or  had  his  subsequent  life  been  devoted 
to  money-getting  instead  of  to  research,  would  anybody 
now  dream  of  ascribing  jealousy  to  Davy?  Assuredly 
not.  Why  should  he  be  jealous  ?  His  reputation  at  this 


340  FRAGMENTS  OF  SCIENCE. 

time  was  almost  without  a  parallel :  his  glory  was  without 
a  cloud.  He  had  added  to  his  other  discoveries  that  of 
Faraday,  and  after  having  been  his  teacher  for  seven  years, 
his  language  to  him  was  this :  "  It  gives  me  great  pleasure 
to  hear  that  you  are  comfortable  at  the  Royal  Institution, 
and  I  trust  that  you  will  not  only  do  something  good  and 
honorable  for  yourself,  but  also  for  science."  This  is  not 
the  language  of  jealousy,  potential  or  actual.  But  the 
chlorine  business  introduced  irritation  and  anger,  to  which, 
and  not  to  any  ignobler  motive,  Davy's  opposition  to  the 
election  of  Faraday  to  the  Royal  Society  is,  I  am  per- 
suaded, to  be  ascribed. 

These  matters  are  touched  upon  with  perfect  candor 
and  becoming  consideration  in  the  volumes  of  Dr.  Bence 
Jones,  but  in  "  society "  they  are  not  always  so  handled. 
Here  a  name  of  noble  intellectual  associations  is  surrounded 
by  injurious  rumors  which  I  would  willingly  scatter  for- 
ever. The  pupil's  magnitude  and  the  splendor  of  his  posi- 
tion are  too  great  and  absolute  to  need  as  a  foil  the  humilia- 
tion of  his  master.  Brothers  in  intellect,  Davy  and  Fara- 
day, however,  could  never  have  become  brothers  in  feeling ; 
their  characters  were  too  unlike.  Davy  loved  the  pomp 
and  circumstance  of  fame,  Faraday  the  inner  consciousness 
that  he  had  fairly  won  renown.  They  were  both  proud 
men.  But  with  Davy  pride  projected  itself  into  the  outer 
world,  while  with  Faraday  it  became  a  steadying  and  dig- 
nifying inward  force.  In  one  great  particular  they  agreed. 
Each  of  them  could  have  turned  his  science  to  immense 
commercial  profit,  but  neither  of  them  did  so.  The  noble 
excitement  of  research,  and  the  delight  of  discovery,  con- 
stituted their  reward.  I  commend  them  to  the  reverence 
which  great  gifts  greatly  exercised  ought  to  inspire.  They 
were  both  ours,  and  through  the  coming  centuries  England 
will  be  able  to  point  with  just  pride  to  the  possession  of 
such  men. 


FARADAY.  341 

The  first  volume  of  the  "  Life  and  Letters  "  reveals  to 
us  the  youth  who  was  to  be  father  to  the  man.  Skilful, 
aspiring,  resolute,  he  grew  steadily  in  knowledge  and  in 
power.  Consciously  or  unconsciously,  the  relation  of  action 
to  reaction  was  ever  present  to  Faraday's  mind.  It  had 
been  fostered  by  his  discovery  of  magnetic  rotations,  and 
it  planted  in  him  more  daring  ideas  of  a  similar  kind.  Mag- 
netism he  knew  could  be  evoked  by  electricity,  and  he 
thought  that  electricity,  in  its  turn,  ought  to  be  capable  of 
evolution  by  magnetism.  On  August  29,  1831,  his  experi- 
ments on  this  subject  began.  He  had  been  fortified  by 
previous  trials,  which,  though  failures,  had  begotten  in- 
stincjts  directing  him  toward  the  truth.  He,  like  every 
strong  worker,  might  at  times  miss  the  outward  object,  but 
he  always  gained  the  inner  light — education  and  expansion. 
Of  this  Faraday's  life  was  a  constant  illustration.  By  No- 
vember he  had  discovered  and  colligated  a  multitude  of 
the  most  wonderful  and  unexpected  phenomena.  He  had 
generated  currents  by  currents ;  currents  by  magnets,  per- 
manent and  transitory;  and  he  afterward  generated  cur- 
rents by  the  earth  itself.  Arago's  "  Magnetism  of  Rota- 
tion," which  had  for  years  offered  itself  as  a  challenge  to 
the  best  scientific  intellects  of  Europe,  now  fell  into  his 
hands.  It  proved  to  be  a  beautiful  but  still  special  illustra- 
tion of  the  great  principle  of  magneto-electric  induction. 
Nothing  equal  to  this,  in  the  way  of  pure  experimental  in- 
quiry, had  previously  been  achieved. 

Electricities  from  various  sources  were  next  examined, 
and  their  differences  and  resemblances  revealed.  He  thus 
assured  himself  of  their  substantial  identity.  He  then  took 
up  conduction,  and  gave  many  striking  illustrations  of  the 
influence  of  fusion  on  conducting  power.  Renouncing  pro- 
fessional work,  from  which  at  this  time  he  might  have  de- 
rived an  income  of  many  thousands  a  year,  he  poured  his 
whole  momentum  into  his  researches.  He  was  long  en- 


342  FRAGMENTS  OF  SCIENCE. 

tangled  in  electro-chemistry.  The  light  .of  law  was  for  a 
time  obscured  by  the  thick  umbrage  of  novel  facts ;  but  he 
finally  emerged  from  his  researches  with  the  great  principle 
of  definite  electro-chemical  decomposition  in  his  hands.  If 
his  discovery  of  magneto-electricity  may  be  ranked  with 
that  of  the  pile  by  Volta,  this  new  discovery  may  almost 
stand  beside  that  of  definite  combining  proportions  in 
chemistry.  He  passed  on  to  static  electricity — its  conduc- 
tion, induction,  and  mode  of  propagation.  He  discovered 
and  illustrated  the  principle  of  inductive  capacity;  and, 
turning  to  theory,  he  asked  himself  how  electrical  attrac- 
tions and  repulsions  are  transmitted.  Are  they,  like  gravity, 
actions  at  a  distance,  or  do  they  require  a  medium  ?  If  the 
former,  then,  like  gravity,  they  will  act  in  straight  lines ;  if 
the  latter,  then,  like  sound  or  light,  they  may  turn  a  corner. 
Faraday  held,  and  his  views  are  gaining  ground,  that  his 
experiments  proved  the  fact  of  curvilinear  propagation,  and 
hence  the  operation  of  a  medium.  Others  denied  this ;  but 
none  can  deny  the  profound  and  philosophic  character  of 
his  leading  thought.1  The  first  volume  of  the  researches 
contains  all  the  papers  here  referred  to. 

Faraday  had  heard  it  stated  that  henceforth  physical 
discovery  would  be  made  solely  by  the  aid  of  mathematics ; 
that  we  had  our  data,  and  needed  only  to  work  deductively. 
Statements  of  a  similar  character  crop  out  from  time  to 
time  in  our  day.  They  arise  from  an  imperfect  acquaintance 
with  the  nature,  present  condition,  and  prospective  vastness 
of  the  field  of  physical  inquiry.  The  tendency  of  natural 
science  doubtless  is  to  bring  all  physical  phenomena  under 
the  dominion  of  mechanical  laws ;  to  give  them,  in  other 
words,  mathematical  expression.  But  our  approach  to  this 
result  is  asymptotic ;  and  for  ages  to  come — possibly  for 

1  In  a  very  remarkable  paper  published  in  PoggendorfFs  Annalen  for 
1857,  Werner  Siemens  develops  and  accepts  Faraday's  theory  of  molecu- 
lar induction. 


FARADAY.  343 

all  the  ages  of  the  human  race — Nature  will  find  room  for 
both  the  philosophical  experimenter  and  the  mathematician. 
Faraday  entered  his  protest  against  the  foregoing  statement 
by  labelling  his  investigations  "  Experimental  Researches 
in  Electricity."  They  were  completed  in  1854,  and  three 
volumes  of  them  have  been  published.  For  the  sake  of 
reference  he  numbered  every  paragraph,  the  last  number 
being  3,362.  In  1859  he  collected  and  published  a  fourth 
volume  of  papers  under  the  title,  "  Experimental  Researches 
in  Chemistry  and  Physics."  Thus  the  apostle  of  experi- 
ment magnified  his  office. 

The  second  volume  of  the  Researches  embraces  memoirs 
on  the  Electricity  of  the  Gymnotus ;  on  the  Source  of  Power 
in  the  Voltaic  Pile ;  on  the  Electricity  evolved  by  the  Friction 
of  Water  and  Steam,  in  which  the  phenomena  and  principles 
of  Sir  William  Armstrong's  Hydro-electric  machine  are 
described  and  developed  ;  a  paper  on  Magnetic  Rotations, 
and  Faraday's  letters  in  relation  to  the  controversy  it 
aroused.  The  contribution  of  the  most  permanent  value 
here  is  that  on  the  Source  of  Power  in  the  Voltaic  Pile.  By 
it  the  Contact  Theory,  pure  and  simple,  was  totally  over- 
thrown, and  the  necessity  of  chemical  action  to  the  main- 
tenance of  the  current  demonstrated. 

The  third  volume  of  the  Researches  opens  with  a  me- 
moir entitled,  "  The  Magnetization  of  Light,  and  the  Illu- 
mination of  Magnetic  Lines  of  Force."  It  is  difficult  even 
now  to  affix  a  definite  meaning  to  this  title ;  but  the  dis- 
covery of  the  rotation  of  the  plane  of  polarization  which  it 
announced  seems  pregnant  with  great  results.  The  writ- 
ings of  William  Thomson  on  the  theoretic  aspects  of  the 
discovery ;  the  excellent  electro-dynamic  measurements  of 
Wilhelm  Weber,  which  are  models  of  experimental  com- 
pleteness and  skill ;  Weber's  labors  in  conjunction  with  his 
lamented  friend  Kohlrausch — above  all,  the  researches  of 
Clerk  Maxwell  on  the  Electro-magnetic  Theory  of  Light — 


344  FRAGMENTS  OF  SCIENCE. 

point  to  that  wonderful  and  mysterious  medium  which  is 
the  vehicle  of  light  and  radiant  heat  as  the  probable  basis 
also  of  magnetic  and  electric  phenomena.  The  hope  of 
such  a  combination  was  first  raised  by  the  discovery  here 
referred  to.1  Faraday  himself  seemed  to  cling  with  partic- 
ular affection  to  this  discovery.  He  felt  that  there  was 
more  in  it  than  he  was  able  to  unfold.  He  predicted  that 
it  would  grow  in  meaning  with  the  growth  of  science.  This 
it  has  done ;  this  it  is  doing  now.  Its  right  interpretation 
will  probably  mark  an  epoch  in  scientific  history. 

Rapidly  following  it  is  the  discovery  of  Diamagnetism, 
or  the  Repulsion  of  Matter  by  a  magnet.  Brugmans  had 
shown  that  bismuth  repelled  a  magnetic  needle.  Here  he 
stopped..  Le  Bailliff  proved  that  antimony  did  the  same. 
Here  he  stopped.  Seebeck,  Becquerel,  and  others,  also 
touched  the  discovery.  These  fragmentary  gleams  excited 
a  momentary  curiosity,  and  were  almost  forgotten,  when 
Faraday,  independently,  alighted  on  the  same  facts ;  and, 
instead  of  stopping,  made  them  the  inlets  to  a  new  and 
vast  region  of  research.  The  value  of  a  discovery  is  to  be 
measured  by  the  intellectual  action  it  calls  forth ;  and  it 
was  Faraday's  good  fortune  to  strike  such  lodes  of  scientific 
truth  as  give  some  of  the  best  intellects  of  the  age  occupa- 
tion. 

The  salient  quality  of  Faraday's  scientific  character  re- 
veals itself  from  beginning  to  end  of  these  volumes  :  a  union 

1  A  letter  addressed  to  me  by  Professor  Weber,  on  the  18th  of  last 
March,  contains  the  following  reference  to  the  connection  here  mentioned : 
"  Die  Hoffnung  einer  solchen  Combination  ist  durch  Faraday's  Entdeckung 
dor  Drehung  der  Polarisationsebene  durch  magnetische  Directionskraft 
zuerst,  und  sodann  durch  die  Uebereinstimmung  derjenigen  Geschwindig- 
keit,  welche  das  Verhaltniss  der  electro-dynamischen  Einheit  zur  electro- 
statischen  ausdriickt,  mit  der  Geschwindigkeit  des  Lichts  angeregt 
worden ;  und  mir  scheint  von  alien  Versuchen,  welche  zur  Verwirklichung 
dieser  Hoffnung  gemacht  worden  sind,  das  von  Efernn  Maxwell  gemachte 
am  erfolgreichsten." 


FARADAY.  345 

of  ardor  and  patience — the  one  prompting  the  attack,  the 
other  holding  him  on  to  it  till  defeat  was  final  or  victory 
assured.  Certainty  in  one  sense  or  the  other  was  necessary 
to  his  peace  of  mind.  The  right  method  of  investigation 
is,  perhaps,  incommunicable  ;  it  depends  on  the  individual 
rather  than  on  the  system,  and  the  mark  is  missed  when 
Faraday's  researches  are  pointed  to  as  merely  illustrative 
of  the  power  of  the  inductive  philosophy.  The  brain  may 
be  filled  with  that  philosophy,  but  without  the  energy  and 
insight  which  this  man  possessed,  and  which  with  him  were 
personal  and  distinctive,  we  should  never  rise  to  the  level 
of  his  achievements.  His  power  is  that  of  individual  genius, 
rather  than  of  philosophic  method ;  the  energy  of  a  strong 
soul  expressing  itself  after  its  own  fashion,  and  acknowl- 
edging no  mediator  between  it  and  Nature. 

The  second  volume  of  the  "  Life  and  Letters,"  like  the 
first,  is  an  historic  treasury  as  regards  Faraday's  work  and 
character,  and  his  scientific  and  social  relations.  It  contains 
letters  from  Humboldt,  Herschel,  Hachette,  De  la  Rive,  Du- 
mas, Liebig,  Melloni,  Becquerel,  Oersted,  PlUcker,  Du  Bois- 
Reymond,  Lord  Melbourne,  Prince  Louis  Napoleon,  and  many 
other  distinguished  men.  I  notice  with  particular  pleasure 
a  letter  from  Sir  John  Herschel  in  reply  to  a  sealed  packet 
addressed  to  him  by  Faraday,  but  which  he  had  permission 
to  open  if  he  pleased.  The  packet  referred  to  one  of  the 
many  unfulfilled  hopes  which  spring  up  in  the  mind  of  fer- 
tile investigators : 

"  Go  on  and  prosper,  *  from  strength  to  strength,'  like  a 
victor  marching  with  assured  step  to  further  conquests ;  and 
be  certain  that  no  voice  will  join  more  heartily  in  the  paeans 
that  already  begin  to  rise,  and  will  speedily  swell  into  a 
shout  of  triumph,  astounding  even  to  yourself,  than  that  of 
J.  F.  W.  Herschel." 

As  an  encourager  of  the  scientific  worker,  this  fine  spirit 
is  still  active. 


346  FRAGMENTS  OF  SCIENCE. 

Faraday's  behavior  to  Melloni  in  1835  merits  a  word  of 
notice.  The  young  man  was  a  political  exile  in  Paris.  He 
had  newly-fashioned  and  applied  the  thermo-electric  pile, 
and  had  obtained  with  it  results  of  the  greatest  importance. 
But  they  were  not  appreciated.  With  the  sickness  of  dis- 
appointed hope,  Melloni  waited  for  the  report  of  the  Com- 
missioners appointed  by  the  Academy  of  Sciences  to  exam- 
ine his  labors.  At  length  he  published  his  researches  in 
the  "  Annales  de  Chimie."  They  thus  fell  into  the  hands 
of  Faraday,  who,  discerning  at  once  their  extraordinary 
merit,  obtained  for  their  author  the  Rumford  Medal  of  the 
Royal  Society.  A  sum  of  money  always  accompanies  this 
medal,  and  the  pecuniary  help  was  at  this  time  even  more 
essential  than  the  mark  of  honor  to  the  young  refugee. 
Melloni' s  gratitude  was  boundless : 

"  Et  vous,  monsieur,"  he  writes  to  Faraday,  "  qui  appar- 
tenez  a  une  societe"  a  laquelle  je  n'avais  rien  oflfert,  vous  qui 
me  connaissiez  &  peine  le  nom ;  vous  n'avez  pas  demande 
si  j'avais  des  ennemis  faibles  ou  puissants,  ni  calcule  quel 
en  6tait  le  nombre ;  mais  vous  avez  parle  pour  Popprime 
Stranger,  pour  celui  qui  n'avait  pas  le  moindre  droit  a  tant 
de  bienveillance,  et  vos  paroles  ont  e'te'  accueillies  favorable- 
ment  par  des  collegues  consciencieux  !  Je  reconnais  bien 
la  des  hommes  dignes  de  leur  noble  mission,  les  ve"ritables 
repre"sentants  de  la  science  d'un  pays  libre  et  ge"n6reux." 

Within  the  prescribed  limits  of  this  article  it  would  be 
impossible  to  give  even  the  slenderest  summary  of  Fara- 
day's correspondence,  or  to  carve  from  it  more  than  the 
merest  fragments  of  his  character.  His  letters,  written  to 
Lord  Melbourne  and  others  in  1836,  regarding  his  pension, 
illustrate  his  uncompromising  independence.  The  Prime 
Minister  had  offended  him,  but  assuredly  the  apology  de- 
manded and  given  was  complete.  I  think  it  certain  that, 
notwithstanding  the  very  full  account  of  this  transaction 
given  by  Dr.  Bence  Jones,  motives  and  influences  were  at 


FARADAY.  347 

work  which  even  now  are  not  entirely  revealed.  The  min- 
ister was  bitterly  attacked,  but  he  bore  the  censure  of  the 
press  with  great  dignity.  Faraday,  while  he  disavowed 
having  either  directly  or  indirectly  furnished  the  matter  of 
those  attacks,  did  not  publicly  exonerate  his  lordship.  The 
Hon.  Caroline  Fox  had  proved  herself  Faraday's  ardent 
friend,  and  it  was  she  who  had  healed  the  breach  between 
the  philosopher  and  the  minister.  She  manifestly  thought 
that  Faraday  ought  to  have  come  forward  in  Lord  Mel- 
bourne's defence,  and  there  is  a  flavor  of  resentment  in  one 
of  her  letters  to  him  on  the  subject.  No  doubt  Faraday  had 
good  grounds  for  his  reticence,  but  they  are  to  me  unknown. 
In  1841  his  health  broke  down  utterly,  and  he  went  to 
Switzerland  with  his  wife  and  brother-iri-law.  His  bodily 
vigor  soon  revived,  and  he  accomplished  feats  of  walking 
respectable  even  for  a  trained  mountaineer.  The  published 
extracts  from  his  Swiss  journal  contain  many  beautiful  and 
touching  allusions.  Amid  references  to  the  tints  of  the 
Jungfrau,  the  blue  rifts  of  the  glaciers,  and  the  noble  Niesen, 
towering  over  the  Lake  of  Thun,  we  come  upon  the  charm- 
ing little  scrap  which  I  have  elsewhere  quoted :  "  Clout-nail 
making  goes  on  here  rather  considerably,  and  is  a  very  neat 
and  pretty  operation  to  observe.  I  love  a  smith's  shop,  and 
any  thing  relating  to  smithery.  My  father  was  a  smith." 
This  is  from  his  journal ;  but  he  is  unconsciously  speaking 
to  somebody — perhaps  to  the  world. 

His  descriptions  of  the  Staub-bach,  Giessbach,  and  of 
the  scenic  effects  of  sky  and  mountain,  are  all  fine  and  sym- 
pathetic. But  amid  it  all,,  and  in  reference  to  it  all,  he  tells 
his  sister  that  "  true  enjoyment  is  from  within,  not  from 
without."  In  those  days  Agassiz  was  living  under  a  slab 
of  gneiss  on  the  glacier  of  the  Aar.  Faraday  met  Forbes 
at  the  Grimsel,  and  arranged  with  him  an  excursion  to  the 
"  H6tel  des  Neuchatelois ; "  but  indisposition  put  the  pro- 
ject out. 


348  FRAGMENTS  OF  SCIENCE. 

From  the  Fort  of  Ham,  in  1843,  Faraday  received  a  let- 
ter addressed  to  him  by  Prince  Louis  Napoleon  Bonaparte. 
He  read  this  letter  to  me  many  years  ago,  and  the  desire, 
shown  in  various  ways  by  the  French  Emperor,  to  turn 
modern  science  to  account,  has  often  reminded  me  of  it 
since.  At  the  age  of  thirty-five  the  prisoner  of  Ham  speaks 
of  "  rendering  his  captivity  less  sad  by  studying  the  great 
discoveries "  which  science  owes  to  Faraday ;  and  he  asks 
a  question  which  reveals  his  cast  of  thought  at  the  time : 
"What  is  the  most  simple  combination  to  give  to  a  voltaic 
battery,  in  order  to  produce  a  spark  capable  of  setting  fire 
to  powder  under  water  or  under  ground  ?  n  Should  the 
necessity  arise,  the  French  Emperor  will  not  lack  at  the 
outset  the  best  appliances  of  modern  science ;  while  we,  I 
fear,  shall  have  to  learn  the  magnitude  of  the  resources  we 
are  now  neglecting  amid  the  pangs  of  actual  war.1 

One  turns  with  renewed  pleasure  to  Faraday's  letters 
to  his  wife,  published  in  the  second  volume.  Here  surely 
the  loving  essence  of  the  man  appears  more  distinctly  than 
anywhere  else.  From  the  house  of  Dr.  Percy,  in  Birming- 
ham, he  writes  thus : 

"Here — even  here — the  moment  I  leave  the  table  I 
wish  I  were  with  you  IN  QUIET.  Oh,  what  happiness  is 
ours  !  My  runs  into  the  world  in  this  way  only  serve  to 
make  me  esteem  that  happiness  the  more." 

And  again  * 

"  We  have  been  to  a  grand  conversazione  in  the  town- 
hall,  and  I  have  now  returned  to  my  room  to  talk  with  you, 
as  the  pleasarstest  and  happiest  thing  that  I  can  do.  Noth- 
ing rests  me  so  much  as  communion  with  you.  I  feel  it 
even  now  as  I  write,  and  catch  myself  saying  the  words 
aloud  as  I  write  them." 

1  The  "  science  "  has  since  been  applied  with  astonishing  effect  by 
those  who  had  studied  it  far  more  thoroughly  than  the  Emperor  oT  the 
French, 


FARADAY,  349 

Take  this,  moreover,  as  indicative  of  his  love  for  Na- 
ture : 

"  After  writing,  I  walk  out  in  the  evening  hand-in-hand 
with  my  dear  wife  to  enjoy  the  sunset ;  for  to  me  who  love 
scenery,  of  all  that  I  have  seen  or  can  see  there  is  none 
surpasses  that  of  heaven.  A  glorious  sunset  brings  with  it 
a  thousand  thoughts  that  delight  me." 

Of  the  numberless  lights  thrown  upon  him  by  the  "  Life 
and  Letters,"  some  fall  upon  his  religion.  In  a  letter  to  a 
lady  he  describes  himself  as  belonging  a  "  a  very  small  and 
despised  sect  of  Christians,  known,  if  known  at  all,  as  San- 
demanians,  and  our  hope  is  founded  on  the  faith  that  is  in 
Christ."  He  adds :  "  I  do  not  think  it  at  all  necessary  to 
tie  the  study  of  the  natural  sciences  and  religion  together, 
and  in  my  intercourse  with  my  fellow-creatures,  that  which 
is  religious,  and  that  which  is  philosophical,  have  ever  been 
two  distinct  things."  He  saw  clearly  the  danger  of  quit- 
ting his  moorings,  and  his  science  became  the  safeguard 
of  his  particular  faith.  For  his  investigations  so  filled  his 
mind  as  to  leave  no  room  for  skeptical  questionings,  thus 
shielding  from  the  assaults  of  philosophy  the  creed  of  his 
youth.  His  religion  was  constitutional  and  hereditary.  It 
was  implied  in  the  eddies  of  his  blood  and  in  the  tremors 
of  his  brain ;  and  however  its  outward  and  visible  form 
might  have  changed,  Faraday  would  still  have  possessed 
its  elemental  constituents — awe,  reverence,  truth,  and  love. 

It  is  worth  inquiring  how  so  profoundly  religious  a  mind, 
and  so  great  a  teacher,  would  be  likely  to  regard  our  pres- 
ent discussions  on  the  subject  of  education.  Faraday 
would  be  a  "  secularist "  were  he  now  alive.  He  had  no 
sympathy  with  those  who  contemn  knowledge  unless  it  be 
accompanied  by  dogma.  A  lecture  delivered  before  the 
City  Philosophical  Society  in  1818,  when  he  was  twenty- 
six  years  of  age,  expresses  the  views  regarding  education 
which  he  entertained  to  the  end  of  his  life.  "  First,  then," 


350  FRAGMENTS  OF  SCIENCE. 

he  says,  "all  theological  considerations  are  banished  from 
the  society,  and  of  course  from  my  remarks  ;  and  whatever 
I  may  say  has  no  reference  to  a  future  state,  or  to  the  means 
which  are  to  be  adopted  in  this  world  in  anticipation  of  it. 
Next,  I  have  no  intention  of  substituting  any  thing  for  re- 
ligion, but  I  wish  to  take  that  part  of  human  nature  whicli 
is  independent  of  it.  Morality,  philosophy,  commerce,  the 
various  institutions  and  habits  of  society,  are  independent 
of  religion,  and  may  exist  either  with  or  without  it.  They 
are  always  the  same,  and  can  dwell  alike  in  the  breasts  of 
those  who  from  opinion  are  entirely  opposed  in  the  set  of 
principles  they  include  in  the  term  religion,  or  in  those  who 
have  none. 

"  To  discriminate  more  closely,  if  possible,  I  will  ob- 
serve that  we  have  no  right  to  judge  religious  opinions,  but 
the  human  nature  of  this  evening  is  that  part  of  man  which 
we  have  a  right  to  judge ;  and  I  think  it  will  be  found,  on 
examination,  that  this  humanity — as  it  may  perhaps  be 
called — will  accord  with  what  I  have  before  described  as 
being  in  our  own  hands  so  improvable  and  perfectible." 

Among  my  old  papers  I  find  the  following  remarks  on 
one  of  my  earliest  dinners  with  Faraday :  "  At  two  o'clock 
he  came  down  for  me.  He,  his  niece,  and  myself,  formed 
the  party.  '  I  never  give  dinners,'  he  said.  '  I  don't  know 
how  to  give  dinners,  and  I  never  dine  out.  But  I  should 
not  like  my  friends  to  attribute  this  to  a  wrong  cause.  I 
act  thus  for  the  sake  of  securing  time  for  work,  and  not 
through  religious  motives,  as  some  imagine.'  He  said 
grace.  I  am  almost  ashamed  to  call  his  prayer  a  '  saying ' 
of  grace.  In  the  language  of  Scripture,  it  might  be  de- 
scribed as  the  petition  of  a  son,  into  whose  heart  God  had 
sent  the  Spirit  of  His  Son,  and  who  with  absolute  trust 
asked  a  blessing  from  his  father.  We  dined  on  roast  beef, 
Yorkshire  pudding,  and  potatoes ;  drank  sherry,  talked  of 
research  and  its  requirements,  and  of  his  habit  of  keeping 


FARADAY.  351 

himself  free  from  the  distractions  of  society.  He  was  bright 
and  joyful— boylike,  in  fact,  though  he  is  now  sixty-two. 
His  work  excites  admiration,  but  contact  with  him  warms 
and  elevates  the  heart.  Here,  surely,  is  a  strong  man.  I 
love  strength,  but  let  me  not  forget  the  example  of  its 
union  with  modesty,  tenderness,  and  sweetness,  in  the  char- 
acter of  Faraday." 

Faraday's  progress  in  discovery,  and  the  salient  points 
of  his  character,  are  well  brought  out  by  the  wise  choice  of 
letters  and  extracts  published  in  these  volumes.  I  will  not 
call  the  labors  of  the  biographer  final.  So  great  a  char- 
acter will  challenge  reconstruction.  In  the  coming  time 
some  sympathetic  spirit,  with  the  requisite  strength,  knowl- 
edge, and  solvent  power,  will,  I  doubt  not,  render  these 
materials  plastic,  give  them  more  perfect  organic  form,  and 
send  through  them,  with  less  of  interruption,  the  currents 
of  Faraday's  life.  "  He  was  too  good  a  man,"  writes  his 
present  biographer,  "  for  me  to  estimate  rightly,  and  too 
great  a  philosopher  for  me  to  understand  thoroughly." 
That  may  be,  but  the  reverent  affection  to  which  we  owe 
the  discovery,  selection,  and  arrangement  of  the  materials 
here  placed  before  us,  is  probably  a  surer  guide  than  mere 
literary  skill.  The  task  of  the  artist  who  may  wish  in 
future  times  to  reproduce  the  real  though  unobtrusive 
grandeur,  the  purity,  beauty,  and  childlike  simplicity  of 
him  whom  we  have  lost,  will  find  his  chief  treasury  already 
provided  for  him  by  Dr.  Bence  Jones's  labor  of  love. 


Library 


XIII. 

AN 

ELEMENTARY  LECTURE  ON  MAGNETISM. 

ADDKESS  TO  THE   TEACHERS  OF  PEIMAET  SCHOOLS  AT  THE  SOUTH 
KENSINGTON  MUSEUM. 

April  30,  1861. 


"  Next  in  order  I  will  proceed  to  discuss  by  what  law  of  Nature  it 
comes  to  pass  that  iron  can  be  attracted  by  that  stone  which  the  Greeks 
call  the  Magnet  from  the  name  of  its  native  place,  because  it  has  its  origin 
within  the  bounds  of  the  country  of  the  Magnesians.  This  stone  is  more 
wondered  at  because  it  often  produces  a  chain  of  [iron]  rings  hanging 
down  from  it.  Thus  you  may  see  five  and  more  suspended  in  succession 
and  tossing  about  in  the  light  airs,  one  always  hanging  from  the  other 
and  attached  to  its  lower  side,  and  each  in  turn  one  from  the  other  ex- 
periencing the  binding  power  of  the  stone :  with  such  a  continued  cur- 
rent its  force  flies  through  all. 

"  In  things  of  this  kind,  many  things  must  be  established  before  you 
can  assign  the  true  law  of  the  thing  in  question,  and  it  must  be  ap- 
proached by  a  very  circuitous  road ;  wherefore  all  the  more  I  call  for  an 
attentive  ear  and  mind." — LUCRETIUS,  DC  Rerum  Natura,  Lib.  VI., 
Munro's  Translation,  p.  317. 

This  lecture  is  a  plain  statement  of  the  elementary  facts  of  magnet- 
ism, of  one  magnetic  theory,  and  of  the  methods  to  be  pursued  in  master- 
ing both.  It  has  already  circulated  among  the  teachers  mentioned  on  its 
title-page,  and  I  had  some  doubts  as  to  the  propriety  of  its  insertion 
here.  But,  on  reading  it,  it  seemed  so  likely  to  be  helpful,  that  my 
scruples  disappeared.  J.  T. 


MAGNETIC    LINES    OF    FORCE. 

From  a  Photograph  by  Professor  MAYER,  Lehigh  University,  United  States. 


XIII. 

A  LECTURE    ON  MAGNETISM. 

WE  have  no  reason  to  believe  that  the  sheep  or  the  dog, 
or,  indeed,  any  of  the  lower  animals,  feel  an  interest  in  the 
laws  by  which  natural  phenomena  are  regulated.  A  herd 
may  be  terrified  by  a  thunder-storm ;  birds  may  go  to  roost, 
and  cattle  return  to  their  stalls  during  a  solar  eclipse ;  but 
neither  birds  nor  cattle,  as  far  as  we  know,  ever  think  of 
inquiring  into  the  causes  of  these  things.  It  is  otherwise 
with  man.  The  presence  of  natural  objects,  the  occurrence 
of  natural  events,  the  varied  appearances  of  the  universe  in 
which  he  dwells,  penetrate  beyond  his  organs  of  sense,  and 
appeal  to  an  inner  power  of  which  the  senses  are  the  mere 
instruments  and  excitants.  No  fact  is  to  him  either  final 
or  original.  He  cannot  limit  himself  to  the  contemplation 
of  it  alone,  but  endeavors  to  ascertain  its  position  in  a 
series  to  which  the  constitution  of  his  mind  assures  him  it 
must  belong.  He  regards  all  that  he  witnesses  in  the 
present  as  the  efflux  and  sequence  of  something  that  has 
gone  before,  and  as  the  source  of  a  system  of  events  which 
is  to  follow.  The  notion  of  spontaneity,  by  which  in  his 
ruder  .state  he  accounted  for  natural  events,  is  abandoned; 
the  idea  that  Nature  is  an  aggregate  of  independent  parts 
also  disappears,  as  the  connection  and  mutual  dependence 
of  physical  powers  become  more  and  more  manifest :  until 
he  is  finally  led,  and  that  chiefly  by  the  science  of  which 
I  happen  this  evening  to  be  the  exponent,  to  regard 


358  FRAGMENTS  OF  SCIENCE. 

Nature  as  an  organic  whole,  as  a  body  each  of  whose 
members  sympathizes  with  the  rest,  changing,  it  is  true, 
from  ages  to  ages,  but  without  one  real  break  of  continuity, 
or  a  single  interruption  of  the  fixed  relations  of  cause  and 
effect. 

The  system  of  things  which  we  call  Nature  is,  however, 
too  vast  and  various  to  be  studied  first-hand  by  any  single 
mind.  As  knowledge  extends  there  is  always  a  tendency 
to  subdivide  the  field  of  investigation,  its  various  parts  be- 
ing taken  up  by  different  individuals,  and  thus  receiving  a 
greater  amount  of  attention  than  could  possibly  be  bestowed 
on  them  if  each  investigator  aimed  at  the  mastery  of  the 
whole.  East,  west,  north,  and  south,  the  human  mind 
pushes  its  conquests ;  but  the  centripetal  form  in  which 
knowledge,  as  a  whole,  advances,  spreading  ever  wider  on 
all  sides,  is  due  in  reality  to  the  exertions  of  individuals, 
each  of  whom  directs  his  efforts,  more  or  less,  along  a  single 
line.  Accepting,  in  many  respects,  his  culture  from  his 
fellow-men,  taking  it  from  spoken  words  and  from  written 
books,  in  some  one  direction,  the  student  of  Nature  must 
actually  touch  his  work.  He  may  otherwise  be  a  dis- 
tributor of  knowledge,  but  not  a  creator,  and  fails  to  attain 
that  vitality  of  thought  and  correctness  of  judgment  which 
direct  and  habitual  contact  with  natural  truth  can  alone 
impart. 

One  large  department  of  the  system  of  Nature  which 
forms  the  chief  subject  of  my  own  studies,  and  to  which  it 
is  my  duty  to  call  your  attention  this  evening,  is  that  of 
physics,  or  natural  philosophy.  This  term  is  large  enough 
to  cover  the  study  of  Nature  generally,  but  it  is  usually 
restricted  to  a  department  which,  perhaps,  lies  closer  to 
our  perceptions  than  any  other.  It  deals  with  the  phe- 
nomena and  laws  of  light  and  heat — with  the  phenomena 
and  laws  of  magnetism  and  electricity — with  those  of 
sound  —  with  the  pressures  and  motions  of  liquids  and 


A  LECTURE   ON  MAGNETISM.  359 

gases,  whether  in  a  state  of  translation  or  of  undulation. 
The  science  of  mechanics  is  a  portion  of  natural  philosophy, 
though  at  present  so  large  as  to  need  the  exclusive  atten- 
tion of  him  who  would  cultivate  it  profoundly.  Astronomy 
is  the  application  of  physics  to  the  motions  of  the  heavenly 
bodies,  the  vastness  of  the  field  causing  it,  however,  to  be 
regarded  as  a  department  in  itself.  In  chemistry  physical 
agents  play  important  parts.  By  heat  and  light  we  cause 
bodies  to  combine,  and  by  heat  and  light  we  decompose 
them.  Electricity  tears  asunder  the  locked  atoms  of  com- 
pounds, through  their  power  of  separating  carbonic  acid  into 
its  constituents  ;  the  solar  beams  build  up  the  whole  vege- 
table world,  and  .by  it  the  animal,  while  the  touch  of  the 
self-same  beams  causes  hydrogen  and  chlorine  to  unite  with 
sudden  explosion  and  form  by  their  combination  a  powerful 
acid.  Thus  physics  and  chemistry  intermingle,  physical 
agents  being  employed  by  the  chemist  as  a  means  to  an 
end ;  while  in  physics  proper  the  laws  and  phenomena  of 
the  agents  themselves,  both  qualitative  and  quantitative, 
are  the  primary  objects  of  attention. 

My  duty  here  to-night  is  to  spend  an  hour  in  telling  how 
this  subject  is  to  be  studied,  and  how  a  knowledge  of  it  is 
to  be  imparted  to  others.  When  first  invited  to  do  this,  I 
hesitated  before  accepting  the  responsibility.  It  would  be 
easy  to  entertain  you  with  an  account  of  what  natural  phi- 
losophy has  accomplished.  I  might  point  to  those  applica- 
tions of  science  regarding  which  we  hear  so  much  in  the 
newspapers,  and  which  we  often  find  mistaken  for  science 
itself.  I  might,  of  course,  ring  changes  on  the  steam- 
engine  and  the  telegraph,  the  electrotype  and  the  photo- 
graph, the  medical  applications  of  physics,  and  the  million 
other  inlets  by  which  scientific  thought  filters  into  prac- 
tical life.  That  would  be  easy  compared  with  the  task 
of  informing  you  how  you  are  to  make  the  study  of  physics 
the  instrument  of  your  own  culture,  how  you  are  to  pos- 


360  FRAGMENTS  OF  SCIENCE. 

sess  its  facts  and  make  them  living"  seeds  which  shall 
take  root  and  grow  in  the  mind,  and  not  lie  like  dead 
lumber  in  the  store-house  of  memory.  This  is  a  task  much 
heavier  than  the  mere  cataloguing  of  scientific  achieve- 
ments ;  and  it  is  one  which,  feeling  my  own  want  of  time 
and  power  to  execute  it  aright,  I  might  well  hesitate  to 
accept. 

But  let  me  sink  excuses,  and  attack  the  work  to  the 
best  of  my  ability.  First  and  foremost,  then,  I  would  ad- 
vise you  to  get  a  knowledge  of  facts  from  actual  observa- 
tion. Facts  looked  at  directly  are  vital ;  when  they  pass 
into  words  half  the  sap  is  taken  out  of  them.  You  wish, 
for  example,  to  get  a  knowledge  of  magnetism ;  well,  pro- 
vide yourself  with  a  good,  book  on  the  subject,  if  you  can, 
but  do  not  be  content  with  what  the  book  tells  you ;  do 
not  be  satisfied  with  its  descriptive  woodcuts ;  see  the 
actual  thing  yourself.  Half  of  our  book-writers  describe 
experiments  which  they  never  made,  and  their  descrip- 
tions often  lack  both  force  and  truth ;  but  no  matter  how 
clever  or  conscientious  they  may  be,  their  written  words 
cannot  supply  the  place  of  actual  observation.  Every  fact 
has  numerous  radiations,  which  are  shorn  off  by  the  man 
who  describes  it.  Go,  then,  to  a  philosophical  instrument- 
maker,  and  give,  according  to  your  means,  for  a  straight 
bar-magnet,  say,  half  a  crown,  or,  if  you  can  afford  it,  five 
shillings  for  a  pair  of  them ;  or  get  a  smith  to  cut  a  length 
of  ten  inches  from  a  bar  of  steel  an  inch  wide  and  half  an 
inch  thick ;  file  its  ends  decently,  harden  it,  and  get  some- 
body like  myself  to  magnetize  it.  Two  bar-magnets  are 
better  than  one.  Procure  some  darning-needles  such  as 
these.  Provide  yourself  also  with  a  little  unspun  silk; 
which  will  give  you  a  suspending  fibre  void  of  torsion ; 
make  a  little  loop  of  paper  or  of  wire,  thus,  and  attach  your 
fibre  to  it.  Do  it  neatly.  In  the  loop  place  your  darning- 
needle,  and  bring  the  two  ends  or  poles,  as  they  are  called, 


A  LECTURE  ON  MAGNETISM.  361 

of  your  magnet  successively  up  to  either  end  of  the  needle. 
Both  the  poles,  you  find,  attract  both  ends  of  the  needle. 
Replace  the  needle  by  a  bit  of  annealed  iron  wire,  the  same 
effects  ensue.  Suspend  successively  little  rods  of  lead, 
copper,  silver,  or  brass,  of  wood,  glass,  ivory,  or  whalebone ; 
the  magnet  produces  no  sensible  effect  upon  any  of  these 
substances.  You  thence  infer  a  special  property  in  the 
case  of  steel  and  iron.  Multiply  your  experiments,  how- 
ever, and  you  will  find  that  some  other  substances  besides 
iron  are  acted  upon  by  your  magnet.  A  rod  of  the  metal 
nickel,  or  of  the  metal  cobalt,  from  which  the  blue  color 
used  by  painters  is  derived,  exhibits  powers  similar  to  those 
observed  with  the  iron  and  steel. 

In  studying  the  character  of  the  force  you  may,  how- 
ever, confine  yourself  to  iron  and  steel,  which  are  always 
at  hand.  Make  your  experiments  with  the  darning-needle 
over  and  over  again ;  operate  on  both  ends  of  the  needle ; 
try  both  ends  of  the  magnet.  Do  not  think  the  work  stu- 
pid ;  you  are  conversing  with  Nature,  and  must  acquire  a 
certain  grace  and  mastery  over  her  language ;  and  these 
practice  can  alone  impart.  Let  every  movement  be  made 
with  care,  and  avoid  slovenliness  from  the  outset.  In  every 
one  of  your  experiments  endeavor  to  feel  the  responsibility 
of  a  moral  agent.  Experiment,  as  I  have  said,  is  the  lan- 
guage by  which  we  address  Nature,  and  through  which  she 
sends  her  replies ;  in  the  use  of  this  language  a  lack  of 
straightforwardness  is  as  possible  and  as  prejudicial  as  in 
the  spoken  language  of  the  tongue.  If  you  wish  to  become 
acquainted  with  the  truth  of  Nature,  you  must  from  the  first 
resolve  to  deal  with  her  sincerely. 

Now  remove  your  needle  from  its  loop,  and  draw  it  from 
end  to  end  along  one  of  the  ends  of  the  magnet ;  resuspend 
it,  and  repeat  your  former  experiment.  You  find  the  result 
different.  You  now  find  that  each  extremity  of  the  magnet 
attracts  one  end  of  the  needle  and  repels  the  other.  The 
16 


362  FRAGMENTS  OF  SCIENCE. 

simple  attraction  observed  in  the  first  instance  is  now  re- 
placed by  a  dual  force.  Repeat  the  experiment  till  you 
have  thoroughly  observed  the  ends  which  attract  and  those 
which  repel  each  other. 

Withdraw  the  magnet  entirely  from  the  vicinity  of  your 
needle,  and  leave  the  latter  freely  suspended  by  its  fibre. 
Shelter  it  as  well  as  you  can  from  currents  of  air,  and  if 
you  have  iron  buttons  on  your  coat  or  a  steel  penknife  in 
your  pocket,  beware  of  their  action.  If  you  work  at  night, 
beware  of  iron  candlesticks,  or  of  brass  ones  with  iron  rods 
inside.  Freed  from  such  disturbances,  the  needle  takes  up 
a  certain  determinate  position.  It  sets  its  length  nearly 
north  and  south.  Draw  it  aside  from  this  position  and  let 
it  go.  After  several  oscillations  it  will  again  come  to  it. 
If  you  have  obtained  your  magnet  from  a  philosophical-in- 
strument maker,  you  will  see  a  mark  on  one  of  its  ends. 
Supposing,  then,  that  you  drew  your  needle  along  the  end 
thus  marked,  and  that  the  eye-end  of  your  needle  was  the 
last  to  quit  the  magnet,  you  will  find  that  the  eye  turns  to 
the  south,  the  point  of  the  needle  turning  toward  the  north. 
Make  sure  of  this,  and  do  not  take  this  statement  on  my 
authority. 

Now  take  a  second  darning-needle  like  the  first,  and 
magnetize  it  in  precisely  the  same  manner:  freely  sus- 
pended it  also  will  turn  its  point  to  the  north  and  its  eye 
to  the  south.  Your  next  step  is  to  examine  the  action  of 
the  two  needles  which  you  have  thus  magnetized  upon  each 
other. 

Take  one  of  them  in  your  hand,  and  leave  the  other  sus- 
pended ;  bring  the  eye-end  of  the  former  near  the  eye-end 
of  the  latter ;  Vthe  suspended  needle  retreats  :  it  is  repelled. 
Make  the  sam0  experiment  with  the  two  points,  you  obtain 
the  same  result,  the  suspended  needle  is  repelled.  Now 
cause  the  dissimilar  ends  to  act  on  each  other — you  have 
attraction — point  attracts  eye  and  eye  attracts  point.  Prove 


A  LECTURE  ON  MAGNETISM.  363 

the  reciprocity  of  this  action  by  removing  the  suspended 
needle,  and  putting  the  other  in  its  place.  You  obtain  the 
same  result.  The  attraction,  then,  is  mutual,  and  the  re- 
pulsion is  mutual,  and  you  have  thus  demonstrated  in  the 
clearest  manner  the  fundamental  law  of  magnetism,  that 
like  poles  repel,  and  that  unlike  poles  attract  each  other. 
You  may  say  that  this  is  all  easily  understood  without  do- 
ing ;  but  do  it,  and  your  knowledge  will  not  be  confined  to 
what  I  have  uttered  here. 

I  have  said  that  one  end  of  your  magnet  has  a  mark 
upon  it ;  lay  several  silk  fibres  together,  so  as  to  get  suffi- 
cient strength,  or  employ  a  thin  silk  ribbon,  and  form  a  loop 
large  enough  to  hold  your  magnet.  Suspend  it ;  it  turns 
its  marked  end  toward  the  north.  This  marked  end  is  that 
which  in  England  is  called  the  north  pole.  If  a  common 
smith  has  made  your  magnet,  it  will  be  convenient  to  deter- 
mine its  north  pole  yourself,  and  to  mark  it  with  a  file. 
You  vary  your  experiments  by  causing  your  magnetized 
darning-needle  to  attract  and  repel  your  large  magnet ;  it 
is  quite  competent  to  do  so.  In  magnetizing  the  needle,  I 
have  supposed  the  eye-end  to  be  the  last  to  quit  the  marked 
end  of  the  magnet ;  that  end  of  the  needle  is  a  south  pole. 
The  end  which  last  quits  the  magnet  is  always  opposed  in 
polarity  to  the  end  of  the  magnet  with  which  it  has  been  in 
contact.  Brought  near  each  other  they  mutually  attract, 
and  thus  demonstrate  that  they  are  unlike  poles. 

You  may  perhaps  learn  all  this  in  a  single  hour ;  but 
spend  several  at  it,  if  necessary;  and  remember,  under- 
standing it  is  not  sufficient:  you  must  obtain  a  manual 
aptitude  in  addressing  Nature.  If  you  speak  to  your  fellow- 
man,  you  are  not  entitled  to  use  jargon.  Bad  experiments 
are  jargon  addressed  to  Nature,  and  just  as  much  to  be  dep- 
recated. A  manual  dexterity  in  illustrating  the  interaction 
of  magnetic  poles  is  of  the  utmost  importance  at  this  stage 
of  your  progress,  and  you  must  not  neglect  attaining  this 


364  FRAGMENTS  OF  SCIENCE. 

power  over  your  implements.  As  you  proceed,  moreover, 
you  will  be  tempted  to  do  more  than  I  can  possibly  suggest. 
Thoughts  will  occur  to  you  which  you  will  endeavor  to  fol- 
low out ;  questions  will  arise  which  you  will  try  to  answer. 
The  same  experiment  may  be  twenty  things  to  twenty 
people.  Having  witnessed  the  action  of  pole  on  pole 
through  the  air,  you  will  perhaps  try  whether  the  magnetic 
power  is  not  to  be  screened  off.  You  use  plates  of  glass, 
\vood,  slate,  pasteboard,  or  gutta-percha,  but  find  them  all 
pervious  to  this  wondrous  force.  One  magnetic  pole  acts 
upon  another  through  these  bodies  as  if  they  were  not 
present.  And  should  you  become  a  patentee  for  the  regu- 
lation of  ships'  compasses,  you  will  not  fall,  as  some  pro- 
jectors have  done,  into  the  error  of  screening  off  the  mag- 
netism of  the  ship  by  the  interposition  of  such  substances. 

If  you  wish  to  teach  a  class  you  must  contrive  that  the 
effects  which  you  have  thus  far  witnessed  for  yourself  shall 
be  witnessed  by  twenty  or  thirty  pupils.  And  here  your 
private  ingenuity  must  come  into  play.  You  will  attach 
bits  of  paper  to  your  needles,  so  as  to  render  their  move- 
ments visible  at  a  distance,  denoting  the  north  and  south 
poles  by  different  colors,  say  green  and  red.  You  may  also 
improve  upon  your  darning-needle.  Take  a  strip  of  sheet- 
steel,  the  rib  of  a  lady's  stays  will  answer,  heat  it  to  vivid 
redness  and  plunge  it  into  cold  water.  It  is  thereby  hard- 
ened, rendered,  in  fact,  almost  as  brittle  as  glass.  Six 
inches  of  this,  magnetized  in  the  manner  of  the  darning- 
needle,  will  be  better  able  to  carry  your  paper  indexes. 
Having  secured  such  a  strip,  you  proceed  thus : 

Magnetize  a  small  sewing-needle  and  determine  its 
poles ;  or,  break  half  an  inch  or  an  inch  off  your  magnetized 
darning-needle,  and  suspend  it  by  a  fine  silk  fibre.  The 
sewing-needle  or  the  fragment  of  the  darning-needle  is  now 
to  be  used  as  a  test-needle  to  examine  the  distribution  of 
the  magnetism  in  your  strip  of  steel.  Hold  the  strip  up- 


A  LECTURE  ON  MAGNETISM.  365 

right  in  your  left  hand,  and  cause  the  test-needle  to  ap- 
proach the  lower  end  of  your  strip;  one  end  is  attracted, 
the  other  is  repelled.  Raise  your  needle  along  the  strip  ; 
its  oscillations,  which  at  first  were  quick,  become  slower ; 
opposite  the  middle  of  the  strip  they  cease  entirely ;  neither 
end  of  the  needle  is  attracted ;  above  the  middle  the  test- 
needle  turns  suddenly  round,  its  other  end  being  now  at- 
tracted. Go  through  the  experiment  thoroughly ;  you  thus 
learn  that  the  entire  lower  half  of  the  strip  attracts  one  end 
of  the  needle,  while  the  entire  upper  half  attracts  the  oppo- 
site end.  Supposing  the  north  end  of  your  little  needle  to 
be  that  attracted  below,  you  infer  that  the  entire  lower  half 
of  your  magnetized  strip  exhibits  south  magnetism,  while 
the  entire  upper  half  exhibits  north  magnetism.  So  far, 
then,  you  have  determined  the  distribution  of  magnetism  in 
your  strip  of  steel. 

You  look  at  this  fact,  you  think  of  it ;  in  its  suggestive- 
ness  the  value  of  the  experiment  chiefly  consists.  The 
thought  arises,  "  What  will  occur  if  I  break  my  strip  of 
steel  across  in  the  middle  ?  Shall  I  obtain  two  magnets, 
each  possessing  a  single  pole  ? "  Try  the  experiment ; 
break  your  strip  of  steel,  and  test  each  half  as  you  tested 
the  whole.  The  mere  presentation  of  its  two  ends  in  suc- 
cession to  your  test-needle  suffices  to  show  you  that  you 
have  not  a  magnet  with  a  single  pole,  that  each  half  pos- 
sesses two  poles  with  a  neutral  point  between  them.  And 
if  you  again  break  the  half  into  two  other  halves,  you  will 
find  that  each  quarter  of  the  original  strip  exhibits  precisely 
the  same  magnetic  distribution  as  the  strip  itself.  You 
may  continue  the  breaking  process ;  no  matter  how  small 
your  fragment  may  be,  it  still  possesses  two  opposite  poles 
and  a  neutral  point  between  them.  Well,  your  hand  ceases 
to  break  where  breaking  becomes  a  mechanical  impossi- 
bility ;  but  does  the  mind  stop  there  ?  No :  you  follow 
the  breaking  process  in  idea  when  you  can  no  longer  realize 


366  FRAGMENTS  OF  SCIENCE. 

it  in  fact ;  your  thoughts  wander  amid  the  very  atoms  of 
your  steel,  and  you  conclude  that  each  atom  is  a  magnet, 
and  that  the  force  exerted  by  the  strip  of  steel  is  the  mere 
summation  or  resultant  of  the  forces  of  its  ultimate  par- 
ticles. 

Here,  then,  is  an  exhibition  of  power  which  we  can  call 
forth  or  cause  to  disappear  at  pleasure.  "We  magnetize  our 
strip  of  steel  by  drawing  it  along  the  pole  of  a  magnet ; 
we  can  demagnetize  it,  or  reverse  its  magnetism,  by  prop- 
erly drawing  it  along  the  same  pole  in  the  opposite  direc- 
tion. What,  then,  is  the  real  nature  of  this  wondrous 
change  ?  What  is  it  that  takes  place  among  the  atoms  of 
the  steel  when  the  substance  is  magnetized  ?  The  question 
leads  us  beyond  the  region  of  sense,  and  into  that  of  imagi- 
nation. This  faculty,  indeed,  is  the  divining-rod  of 'the  man 
of  science.  Not,  however,  an  imagination  which  catches 
its  creations  from  the  air,  but  one  informed  and  inspired  by 
facts,  capable  of  seizing  firmly  on  a  physical  image  as  a 
principle,  of  discerning  its  consequences,  and  of  devising 
means  whereby  these  forecasts  of  thought  may  be  brought 
to  an  experimental  test.  If  such  a  principle  be  adequate  to 
account  for  all  the  phenomena,  if  from  an  assumed  cause 
the  observed  facts  necessarily  follow,  we  call  the  assump- 
tion a  theory,  and,  once  possessing  it,  we  can  not  only  re- 
vive at  pleasure  facts  already  known,  but  we  can  predict 
others  which  we  have  never  seen.  Thus,  then,  in  the  prose- 
cution of  physical  science,  our  powers  of  observation,  mem- 
ory, imagination,  and  inference,  are  all  drawn  upon.  We 
observe  facts  and  store  them  up ;  imagination  broods  upon 
these  memories,  and  by  the  aid  of  reason  tries  to  discern 
their  interdependence.  The  theoretic  principle  flashes,  or 
slowly  dawns  upon  the  mind,  and  then  the  deductive  fac- 
ulty interposes  to  carry  out  the  principle  to  its  logical  con- 
sequences. A  perfect  theory  gives  dominion  over  natural 
facts;  and  even  an  assumption  which  can  only  partially 


A  LECTURE  ON  MAGNETISM.  367 

stand  the  test  of  a  comparison  with  facts,  may  be  of  emi- 
nent use  in  enabling  us  to  connect  and  classify  groups  of 
phenomena.  The  theory  of  magnetic  fluids  is  of  this  latter 
character,  and  with  it  we  must  now  make  ourselves  familiar. 

With  the  view  of  stamping  the  thing  more  firmly  on 
your  minds,  I  will  make  use  of  a  strong  and  vivid  image. 
In  optics,  red  and  green  are  called  complementary  colors ; 
their  mixture  produces  white.  Now  I  ask  you  to  imagine 
each  of  these  colors  to  possess  a  self-repulsive  power ;  that 
red  repels  red,  and  that  green  repels  green ;  but  that  red 
attracts  green  and  green  attracts  red,  the  attraction  of  the 
dissimilar  colors  being  equal  to  the  repulsion  of  the  similar 
ones.  Imagine  the  two  colors  mixed  so  as  to  produce 
white,  and  suppose  two  strips  of  wood  painted  with  this 
white ;  what  will  be  their  action  upon  each  other  ?  Sus- 
pend one  of  them  freely  as  we  suspended  our  darning- 
needle,  and  bring  the  other  near  it ;  what  will  occur  ?  The 
red  component  of  the  strip  you  hold  in  your  hand  will  re- 
pel the  red  component  of  your  suspended  strip,  but  then  it 
will  attract  the  green ;  and  the  forces  being  equal  they  neu- 
tralize each  other..  In  fact,  the  least  reflection  shows  you 
that  the  strips  will  be  as  indifferent  to  each  other  as  two 
unmagnetized  darning-needles  would  be  under  the  same 
circumstances. 

But  suppose,  instead  of  mixing  the  colors,  we  painted 
one  half  of  each  strip  from  centre  to  end  red,  and  the  other 
half  green,  it  is  perfectly  manifest  that  the  two  strips  would 
now  behave  toward  each  other  exactly  as  our  two  magnet- 
ized darning-needles — the  red  end  would  repel  the  red  and 
attract  the  green,  the  green  would  repel  the  green  and  at- 
tract the  red ;  so  that,  assuming  two  colors  thus  related  to 
each  other,  we  could  by  their  mixture  produce  the  neutral- 
ity of  an  unmagnetized  body,  while  by  their  separation  we 
could  produce  the  duality  of  action  of  magnetized  bodies. 

But  you  have  already  anticipated  a  defect  in  my  con- 


368  FRAGMENTS  OF  SCIENCE. 

ception ;  for  if  we  break  one  of  our  strips  of  wood  in  the 
middle  we  have  one  half  entirely  red  and  the  other  entirely 
green,  and  with  these  it  would  be  impossible  to  imitate  the 
action  of  our  broken  magnet.  How,  then,  must  we  modify 
our  conception?  We  must  evidently  suppose  each  atom 
of  wood  painted  green  on  one  face  and  red  on  the  opposite 
one.  If  this  were  done  the  resultant  action  of  all  the  atoms 
would  exactly  resemble  the  action  of  a  magnet.  Here,  also, 
if  the  two  opposite  colors  of  each  atom  could  be  caused 
to  mix  so  as  to  produce  white,  we  should  have,  as  before, 
perfect  neutrality. 

Substitute  in  your  minds  for  these  two  self-repellant 
and  mutually  attractive  colors  two  invisible  self-repellant 
and  mutually  attractive  fluids,  which  in  ordinary  steel  are 
mixed  to  form  a  neutral  compound,  but  which  the  act  of 
magnetization  separates  from  each  other,  placing  the  oppo- 
site fluids  on  the  opposite  faces  of  each  atom,  and  you  have 
a  perfectly  distinct  conception  of  the  celebrated  theory  of 
magnetic  fluids.  The  strength  of  the  magnetism  excited  is 
supposed  to  be  proportional  to  the  quantity  of  neutral  fluid 
decomposed.  According  to  this  theory  nothing  is  actually 
transferred  from  the  exciting  magnet  to  the  excited  steel. 
The  act  of  magnetization  consists  in  the  forcible  separation 
of  two  powers  which  existed  in  the  steel  before  it  was  mag- 
netized, but  which  then  neutralized  each  other  by  their  coa- 
lescence. And  if  you  test  your  magnet  after  it  has  excited 
a  hundred  pieces  of  steel,  you  will  find  that  it  has  lost  no 
force — no  more,  indeed,  than  I  should  lose  had  my  words  such 
a  magnetic  influence  on  your  minds,  as  to  excite  in  them  a 
strong  resolve  to  study  natural  philosophy.  I  should,  in 
fact,  be  the  gainer  by  my  own  utterance  and  by  the  reac- 
tion of  your  strength  ;  and  so  also  the  magnet  is  the  gainer 
by  the  reaction  of  the  body  which  it  magnetizes. 

Look  now  to  your  excited  piece  of  steel ;  figure  each 
atom  to  your  minds  with  its  opposed  fluids  spread  over  its 


A  LECTURE  ON  MAGNETISM.  369 

opposite  faces.  How  can  this  state  of  tilings  be  perma- 
nent ?  The  fluids,  by  hypothesis,  attract  each  other ; 
what,  then,  keeps  them  apart  ?  Why  do  they  not  instantly 
rush  together  across  the  equator  of  the  atom,  and  thus  neu- 
tralize each  other  ?  To  meet  this  question,  philosophers 
have  been  obliged  to  infer  the  existence  of  a  special  force 
which  holds  the  fluids  asunder.  They  call  it  coercive 
force •  and  it  is  found  that  those  kinds  of  steel  which  offer 
most  resistance  to  being  magnetized,  which  require  the 
greatest  amount  of  coercion  to  tear  their  fluids  asunder, 
are  the  very  ones  which  offer  the  greatest  resistance  to  the 
reunion  of  the  fluids  after  they  have  been  once  separated. 
Such  kinds  of  steel  are  most  suited  to  the  formation  of  per- 
manent magnets.  It  is  manifest,  indeed,  that  without 
coercive  force  a  permanent  magnet  -would  not  be  at  all  pos- 
sible. 

You  have  not  forgotten  that,  previous  to  magnetizing  your 
darning-needle,  both  its  ends  were  attracted  by  your  mag- 
net 5  and  that  both  ends  of  your  bit  of  iron  wire  were  acted 
upon  in  the  same  way.  Probably  also  long  before  this  you 
will  have  dipped  the  end  of  your  magnet  among  iron  filings, 
and  observed  how  they  cling  to  it,  or  into  a  nail-box,  and 
found  how  it  drags  the  nails  after  it.  I  know  very  well 
that  if  you  are  not  the  slaves  of  routine,  you  will  have  by 
this  time  done  many  things  that  I  have  not  told  you  to  do, 
and  thus  multiplied  your  experience  beyond  what  I  have 
indicated.  You  are  almost  sure  to  have  caused  a  bit  of 
iron  to  hang  from  the  end  of  your  magnet,  and  you  have 
probably  succeeded  in  causing  a  second  piece  to  attach 
itself  to  the  first,  a  third  to  the  second ;  until  finally  the 
force  has  become  too  feeble  to  bear  the  weight  of  more. 
If  you  have  operated  with  nails,  you  may  have  observed 
that  the  points  and  edges  hold  together  with  the  greatest 
tenacity ;  and  that  a  bit  of  iron  clings  more  firmly  to  the 
corner  of  your  magnet  than  to  one  of  its  flat  surfaces.  In 


370  FRAGMENTS  OF  SCIENCE. 

short,  you  will,  in  all  likelihood,  have  enriched  your  expe- 
rience in  many  ways  without  any  special  direction  from 
me. 

Well,  the  magnet  attracts  the  nail,  and  that  nail  attracts 
a  second  one.  This  proves  that  the  nail  in  contact  with 
the  magnet  has  had  the  magnetic  quality  developed  in  it 
by  that  contact.  If  it  be  withdrawn  from  the  magnet,  its 
power  to  attract  its  fellow-nail  ceases.  Contact,  however, 
is  not  necessary.  A  sheet  of  glass  or  paper,  or  a  space 
of  air,  may  exist  between  the  magnet  and  the  nail ;  the 
latter  is  still  magnetized,  though  not  so  forcibly  as  when 
in  actual  contact.  The  nail  then  presented  to  the  magnet 
is  itself  a  temporary  magnet.  That  end  which  is  turned 
toward  the  magnetic  pole  has  the  opposite  magnetism  of 
the  pole  which  excites  it ;  the  end  most  remote  from  the 
pole  has  the  same  magnetism  as  the  pole  itself,  and  be- 
tween the  two  poles  the  nail,  like  the  magnet,  possesses  a 
magnetic  equator. 

Conversant  as  you  now  are  with  the  theory  of  magnetic 
fluids,  you  have  already,  I  doubt  not,  anticipated  me  in 
imagining  the  exact  condition  of  the  iron  under  the  in- 
fluence of  the  magnet.  You  picture  the  iron  as  possessing 
the  neutral  fluid  in  abundance,  you  picture  the  magnetic 
pole,  when  brought  near,  decomposing  the  fluid  ;  repelling 
the  fluid  of  a  like  kind  with  itself,  and  attracting  the  unlike 
fluid  ;  thus  exciting  in  the  parts  of  the  iron  nearest  to  itself 
the  opposite  polarity.  But  the  iron  is  incapable  of  becoming 
a  permanent  magnet.  It  only  shows  its  virtue  as  long  as 
the  magnet  acts  upon  it.  "What,  then,  does  the  iron  lack 
which  the  steel  possesses  ?  It  lacks  coercive  force.  Its 
fluids  are  separated  with  ease,  but,  once  the  separating 
cause  is  removed,  they  flow  together  again  and  neutrality 
is  restored.  Your  imagination  must  be  quite  nimble  in 
picturing  these  changes.  You  must  be  able  to  see  the 
fluids  dividing  and  reuniting  according  as  the  magnet  is 


A  LECTURE   ON  MAGNETISM.  371 

brought  near  or  withdrawn.  Fixing  a  definite  pole  in  your 
imagination,  you  must  picture  the  precise  arrangement  of 
the  two  fluids  with  reference  to  this  pole.  And  you  must 
not  only  be  well  drilled  in  the  use  of  this  mental  imagery 
yourself,  but  you  must  be  able  to  arouse  the  same  pictures 
in  the  minds  of  your  pupils,  and  satisfy  yourself  that  they 
possess  this  power  of  placing  actually  before  themselves 
magnets  and  iron  in  various  positions,  and  describing  the 
exact  magnetic  state  of  the  iron  in  each  particular  case. 
The  mere  facts  of  magnetism  will  have  their  interest  im- 
mensely augmented  by  an  acquaintance  with  those  hidden 
principles  whereon  the  facts  depend.  Still,  wrhile  you  use 
this  theory  of  magnetic  fluids  to  track  out  the  phenomena 
and  link  them  together,  be  sure  to  tell  your  pupils  that  it 
is  to  be  regarded  as  a  symbol  merely — a  symbol,  more- 
over, which  is  incompetent  to  cover  all  the  facts,1  but  which 
does  good  practical  service  while  we  are  waiting  for  the 
actual  truth. 

This  state  of  excitement  into  which  the  soft  iron  is 
thrown  by  the  influence  of  the  magnet,  is  sometimes  called 
"  magnetization  by  influence."  More  commonly,  however, 
the  magnetism  is  said  to  be  "  induced "  in  the  soft  iron, 
and  hence  this  way  of  magnetizing  is  called  "magnetic 
induction."  Now,  there  is  nothing  theoretically  perfect  in 
Nature  :  there  is  no  iron  so  soft  as  not  to  possess  a  certain 
amount  of  coercive  force,  and  no  steel  so  hard  as  not  to  be 
capable,  in  some  degree,  of  magnetic  induction.  The 
quality  of  steel  is  in  some  measure  possessed  by  iron,  and 
the  quality  of  iron  is  shared  in  some  degree  by  steel.  It  is 
in  virtue  of  this  latter  fact  that  the  unmagnetized  darning- 

1  This  theory  breaks  down  when  applied  to  diamagnetic  bodies,  which 
are  repelled  by  magnets.  Like  soft  iron,  such  bodies  are  thrown  into  a 
state  of  temporary  excitement  in  virtue  of  which  they  are  repelled,  but 
any  attempt  to  explain  such  a  repulsion  by  the  decomposition  of  a  fluid 
will  demonstrate  its  own  futility. 


372  FRAGMENTS  OF  SCIENCE. 

needle  was  attracted  in  your  first  experiment ;  and  from 
this  you  may  at  once  deduce  the  consequence  that,  after  the 
steel  has  been  magnetized,  the  repulsive  action  of  a  magnet 
must  be  always  less  than  its  attractive  action.  For  the 
repulsion  is  opposed  by  the  inductive  action  of  the  magnet 
on  the  steel,  while  the  attraction  is  assisted  by  the  same 
inductive  action.  Make  this  clear  to  your  minds,  and 
verify  it  by  your  experiments.  In  some  cases  you  can 
actually  make  the  attraction  due  to  the  temporary  mag- 
netism overbalance  the  repulsion  due  to  the  permanent 
magnetism,  and  thus  cause  two  poles  of  the  same  kind 
apparently  to  attract  each  other.  "When,  however,  good 
hard  magnets  act  on  each  other  from  a  sufficient  distance, 
the  inductive  action  practically  vanishes,  and  the  repulsion 
of  like  poles  is  sensibly  equal  to  the  attraction  of  unlike 
ones. 

I  dwell  thus  long  on  elementary  principles,  because 
they  are  of  the  first  importance,  and  it  is  the  temptation 
of  this  age  of  unhealthy  cramming  to  neglect  them.  Now 
follow  me  a  little  further.  In  examining  the  distribution 
of  magnetism  in  your  strip  of  steel,  you  raised  the  needle 
slowly  from  bottom  to  top,  and  found  what  we  called  a 
neutral  point  at  the  centre.  Now  does  the  magnet  really 
exert  no  influence  on  the  pole  presented  to  its  centre  ? 
Let  us  see. 

FIG.  1. 


I  -IN 


Let  S  N,  Fig.  1,  be  your  magnet,  and  let  n  represent  a 
particle  of  north  magnetism  placed  exactly  opposite  the 


A  LECTUEE  ON  MAGNETISM.  373 

middle  of  the  magnet.  Of  course  this  is  an  imaginary  case, 
as  you  can  never  in  reality  thus  detach  your  north  mag- 
netism from  its  neighbor.  What  is  the  action  of  the  two 
poles  of  the  magnet  on  n  ?  Your  reply  will  of  course  be 
that  the  pole  S  attracts  n  while  the  pole  N  repels  it. 
Let  the  magnitude  and  direction  of  the  attraction  be  ex- 
pressed by  the  line  n  m,  and  the  magnitude  and  direction 
of  the  repulsion  by  the  line  n  o.  Now  the  particle  n  being 
equally  distant  from  S  and  N,  the  line  n  o,  expressing  the 
repulsion,  will  be  equal  to  m  n,  which  expresses  the  attrac- 
tion, and  the  particle  ny  acted  upon  by  two  such  forces, 
must  evidently  move  in  the  direction  p  n,  exactly  midway 
between  m  n  and  n  o.  Hence  you  see  that,  although  there 
is  no  tendency  of  the  particle  n  to  move  toward  the  mag- 
netic equator,  there  is  a  tendency  on  its  part  to  -move 
parallel  to  the  magnet.  If  instead  of  a  particle  of  north 
magnetism  we  placed  a  particle  of  south  magnetism  op- 
posite to  the  magnetic  equator,  it  would  evidently  be  urged 
along  the  line  n  q  ;  and  if  instead  of  two  separate  particles 
of  magnetism  we  place  a  little  magnetic  needle,  containing 
both  north  and  south  magnetism,  opposite  the  magnetic 
equator,  its  south  pole  being  urged  along  n  q,  and  its  north 
along  n  p,  the  little  needle  will  be  compelled  to  set  itself 
parallel  to  the  magnet  S  N.  Make  the  experiment,  and 
satisfy  yourselves  that  this  is  the  case. 

Substitute  for  your  magnetic  needle  a  bit  of  iron  wire, 
devoid  of  permanent  magnetism,  and  it  will  set  itself  ex- 
actly as  the  needle  does.  Acted  upon  by  the  magnet,  the 
wire,  as  you  know,  becomes  a  magnet  and  behaves  as  such  ; 
it  will,  of  course,  turn  its  north  pole  toward  p9  and  south 
pole  toward  £,  just  like  the  needle. 

But  supposing  you  shift  the  position  of  your  particle  of 
north  magnetism,  and  bring  it  nearer  to  one  end  of  your 
magnet  than  to  the  other,  the  forces  acting  on  the  particle 
are  no  longer  equal ;  the  nearest  pole  of  the  magnet  will 


374  FRAGMENTS  OF  SCIENCE. 

act  more  powerfully  on  the  particle  than  the  more  distant 
one.  Let  S  N,  Fig.  2,  be  the  magnet  and  n  the  particle 
of  north  magnetism  in  its  new  position.  Well,  it  is 
repelled  by  N,  and  attracted  by  S.  Let  the  repulsion  be 
represented  in  magnitude  and  direction  by  the  line  n  o, 
and* the  attraction  by  the  shorter  line  n  m.  The  resultant 
of  these  two  forces  will  be  found  by  completing  the  par- 
allelogram m  n  o  p,  and  drawing  its  diagonal  n  p.  Along 
n  p,  then,  a  particle  of  north  magnetism  would  be  urged 
by  the  simultaneous  action  of  S  and  N.  Substituting  a 


particle  of  south  magnetism  for  n,  the  same  reasoning 
would  lead  to  the  conclusion  that  the  particle  would  be 
urged  along  n  q,  and  if  we  place  at  n  a  short  magnetic 
needle,  its  north  pole  will  be  urged  along  n  p,  its  south 
pole  along  n  q,  and  the  ouly  position  possible  to  the 
needle,  thus  acted  on,  is  along  the  line  p  q,  which,  as  you 
see,  is  no  longer  parallel  to  the  magnet.  Verify  this  by 
actual  experiment. 

In  this  way  we  might  go  round  the  entire  magnet,  and 
considering  its  two  poles  as  two  centres  from  which  the 
force  emanates,  we  could,  in  accordance  with  ordinary  me- 
chanical principles,  assign  a  definite  direction  to  the  mag- 
netic needle  at  every  particular  place.  And  substituting, 
as  before,  a  bit  of  iron  wire  for  the  magnetic  needle,  the 
positions  of  both  will  be  the  same. 


A  LECTURE  ON  MAGNETISM.  375 

Now,  I  think,  without  further  preface,  you  will  be  able 
to  comprehend  for  yourselves,  and  explain  to  others,  one 
of  the. most  interesting  effects  in  the  whole  domain  of 
magnetism.  Iron  filings  you  know  are  particles  of  iron, 
irregular  in  shape,  being  longer  in  some  directions  than  in 
others.  For  the  present  experiment,  moreover,  instead  of 
the  iron  filings,  very  small  scraps  of  thin  iron  wire  might  be 
employed.  I  place  a  sheet  of  paper  over  the  magnet ;  it  is 
all  the  better  if  the  paper  be  stretched  on  a  wooden  frame, 
as  this  enables  us  to  keep  it  quite  level.  I  scatter  the 
filings,  or  the  scraps  of  wire,  from  a  sieve  upon  the  paper, 
and  tap  the  latter  gently,  so  as  to  liberate  the  particles  for 
a  moment  from  its  friction.  The  magnet  acts  on  the  filings 
through  the  paper,  and  see  how  it  arranges  them  !  They 
embrace  the  magnet  in  a  series  of  beautiful  curves,  which 
are  technically  called  magnetic  curves,  or  lines  of  magnetic 
force.  Does  the  meaning  of  these  lines  yet  flash  upon 
you  ?  Set  your  magnetic  needle  or  your  suspended  bit  of 
wire  at  any  point  of  one  of  the  curves,  and  you  will  find 
the  direction  of  the  needle  or  of  the  wire  to  be  exactly  that 
of  the  particle  of  iron,  or  of  the  magnetic  curve  at  the 
point.  Go  round  and  round  the  magnet ;  the  direction  of 
your  needle  always  coincides  with  the  direction  of  the  curve 
on  which  it  is  placed.  These,  then,  are  the  lines  along 
which  a  particle  of  south  magnetism,  if  you  could  detach  it, 
would  move  to  the  north  pole,  and  a  bit  of  north  magnetism 
to  the  south  pole ;  they  are  the  lines  along  which  the  de- 
composition of  the  neutral  fluid  takes  place,  and  in  the  case 
of  the  magnetic  needle,  one  of  its  poles  being  urged  in  one 
direction,  and  the  other  pole  in  the  opposite  direction,  the 
needle  must  necessarily  set  itself  as  a  tangent  to  the  curve. 
I  will  not  seek  to  simplify  this  subject  further.  If  there 
be  any  thing  obscure  or  confused  or  incomplete  in  my 
statement,  you  ought  now,  by  patient  thought,  to  be  able 
to  clear,  away  the  obscurity,  to  reduce  the  confusion  to 


376  FRAGMENTS  ,OF  SCIENCE. 


order,  and  to  supply  what  is  needed  to  render  the  explana- 
tion complete.  Do  not  quit  the  subject  until  you  thor- 
oughly understand  it ;  and  if  you  are  able  to  look  with 
your  mind's  eye  at  the  play  of  forces  around  a  magnet,  and 
see  distinctly  the  operation  of  those  forces  in  the  produc- 
tion of  the  magnetic  curves,  the  time  which  we  have  spent 
together  has  not  been  spent  in  vain. 

In  this  thorough  manner  we  must  master  our  materials, 
reason  upon  them,  and,  by  determined  study,  attain  to  clear- 
ness of  conception.  Facts  thus  dealt  with  exercise  an 
expansive  force  upon  the  boundaries  of  thought;  they 
widen  the  mind  to  generalization.  We  soon  recognize  a 
brotherhood  between  the  larger  phenomena  of  Nature  and 
the  minute  effects  which  we  have  observed  in  our  private 
chambers.  Why,  we  inquire,  does  the  magnetic  needle  set 
north  and  south  ?  Evidently  it  is  compelled  to  do  so  by 
the  earth;  the  great  globe  which  we  inherit  is  itself  a 
magnet.  Let  us  learn  a  little  more  about  it.  By  means  of 
a  bit  of  wax  or  otherwise  attach  your  silk  fibre  to  your 
magnetic  needle  by  a  single  point  at  its  middle,  the  needle 
will  thus  be  uninterfered  with  by  the  paper  loop,  and  will 
enjoy  to  some  extent  a  power  of  dipping  its  point  or  its 
eye  below  the  horizon.  Lay  your  magnet  on  a  table,  and 
hold  the  needle  over  the  equator  of  the  magnet.  The 
needle  sets  horizontal.  Move  it  toward  the  north  end  of 
the  magnet;  the  south  end  of  the  needle  dips,  the  dip 
augmenting  as  you  approach  the  north  pole,  over  which 
the  needle,  if  free  to  move,  will  set  itself  exactly  vertical. 
Move  it  back  to  the  centre,  it  resumes  its  horizontally ; 
pass  it  on  toward  the  south  pole,  its  north  end  now  dips, 
and  directly  over  the  south  pole  the  needle  becomes  ver- 
tical, its  north  end  being  now  turned  downward.  Thus 
we  learn  that  on  the  one  side  of  the  magnetic  equator  the 
north  end  of  the  needle  dips ;  on  the  other  side  the  south 
end  dips,  the  dip  varying  from  nothing  to  ninety  degrees.  If 


A  LECTURE  ON  MAGNETISM.  377 

we  go  to  the  equatorial  regions  of  the  earth  with  a  suit- 
ably-suspended needle,  we  shall  find  there  the  position  of 
the  needle  horizontal.  If  we  sail  north,  one  end  of  the 
needle  dips ;  if  we  sail  south,  the  opposite  end  dips ;  and 
over  the  north  or  south  terrestrial  magnetic  pole  the  needle 
sets  vertical.  The  south  magnetic  pole  has  not  yet  been 
found,  but  Sir  James  Ross  discovered  the  north  magnetic 
pole  on  the  1st  of  June,  1831.  In  this  manner  we  estab- 
lish a  complete  parallelism  between  the  action  of  the  earth 
and  that  of  an  ordinary  magnet. 

The  terrestrial  magnetic  poles  do  not  coincide  with  the 
geographical  ones  ;  nor  does  the  earth's  magnetic  equator 
quite  coincide  with  the  geographical  equator.  The  direc- 
tion of  the  magnetic  needle  in  London,  which  is  called  the 
magnetic  meridian,  encloses  an  angle  of  24  degrees  with 
the  true  astronomical  meridian,  this  angle  being  called  the 
Declination  of  the  needle  for  London.  The  north  pole  of 
the  needle  now  lies  to  the  west  of  the  true  meridian ;  the 
declination  is  westerly.  In  the  year  1660,  however,  the 
declination  was  nothing,  while  before  that  time  it  was 
easterly.  All  this  proves  that  the  earth's  magnetic  con- 
stituents are  gradually  changing  their  distribution.  This 
change  is  very  slow ;  it  is  technically  called  the  secular 
change,  and  the  observation  of  it  has  not  yet  extended  over 
a  sufficient  period  of  -time  to  enable  us  to  guess,  even  ap- 
proximately, at  its  laws. 

Having  thus  discovered,  to  some  extent,  the  secret  of 
the  earth's  power,  we  can  turn  it  to  account.  I  hold  in  my 
hand  a  poker  formed  of  good  soft  iron ;  it  is  now  in  the 
line  of  dip,  a  tangent,  in  fact,  to  the  earth's  line  of  magnetic 
force.  The  earth,  acting  as  a  magnet,  is  at  this  moment 
constraining  the  two  fluids  of  the  poker  to  separate,  making 
the  lower  end  of  the  poker  a  north  pole,  and  the  upper 
end  a  south  pole.  Mark  the  experiment :  I  hold  the  knob 
uppermost,  and  it  attracts  the  north  end  of  a  magnetic 


378  FRAGMENTS  OF  SCIENCE. 

needle.  I  now  reverse  the  poker,  bringing  its  knob  under- 
most ;  the  knob  is  now  a  north  pole  and  attracts  the  south 
end  of  a  magnetic  needle.  Get  such  a  poker  and  carefully 
repeat  this  experiment ;  satisfy  yourselves  that  the  fluids 
shift  their  position  according  to  the  manner  in  which  the 
poker  is  presented  to  the  earth.  It  has  already  been  stated 
that  the  softest  iron  possesses  a  certain  amount  of  coercive 
force.  The  earth,  at  this  moment,  finds  in  this  force  an  an- 
tagonist which  opposes  the  full  decomposition  of  the  neu- 
tral fluid.  The  component  fluids  may  be  figured  as  meet- 
ing an  amount  of  friction,  or  possessing  an  amount  of  ad- 
hesion, which  prevents  them  from  gliding  over  the  atoms 
of  the  poker.  Can  we  assist  the  earth  in  this  case  ?  If  we 
wish  to  remove  the  residue  of  a  powder  from  the  interior 
surface  of  a  glass  to  which  the  powder  clings,  we  invert 
the  glass,  tap  it,  loosen  the  hold  of  the  powder,  and  thus 
enable  the  force  of  gravity  to  pull  it  down.  So  also  by 
tapping  the  end  of  the  poker  we  loosen  the  adhesion  of 
the  fluid  to  the  atoms  and  enable  the  earth  to  pull  them 
apart.  But,  what  is  the  consequence?  The  portion  of 
fluid  which  has  been  thus  forcibly  dragged  over  the  atoms 
refuses  to  return  when  the  poker  has  been  removed 
from  the  line  of  dip;  the  iron,  as  you  see,  has  become 
a  permanent  magnet.  By  reversing  its  position  and 
tapping  it  again  we  reverse  its  magnetism.  A  thoughtful 
and  competent  teacher  will  well  know  how  to  place  these 
remarkable  facts  before  his  pupils  in  a  manner  which  will 
excite  their  interest;  he  will  know,  and  if  not,  will  try  to 
learn,  how,  by  the  use  of  sensible  images,  more  or  less  gross, 
to  give  those  he  teaches  definite  conceptions,  purifying 
these  conceptions  more  and  more  as  the  minds  of  his  pupils 
become  more  capable  of  abstraction.  He  will  cause  his 
logic  to  run  like  a  line  of  light  through  these  images,  and 
by  thus  acting  he  will  cause  his  boys  to  march  at  his 
side  with  a  profit  and  a  joy,  which  the  mere  exhibition  of 


A  LECTURE   ON  MAGNETISM.  379 

facts  without  principles,  or  the  appeal  to  the  bodily  senses 
and  the  power  of  memory  alone,  could  never  inspire. 


As  an  expansion  of  the  note  at  page  371,  the  following  extract  may 
find  a  place  here : 

"  It  is  well  known  that  a  voltaic  current  exerts  an  attractive  force 
upon  a  second  current,  flowing  in  the  same  direction  ;  and  that  when  the 
directions  are  opposed  to  each  other  the  force  exerted  is  a  repulsive  one. 
By  coiling  wires  into  spirals,  Ampere  was  enabled  to  make  them  produce 
all  the  phenomena  of  attraction  and  repulsion  exhibited  by  magnets,  and 
from  this  it  was  but  a  step  to  his  celebrated  theory  of  molecular  cur- 
rents. He  supposed  the  molecules  of  a  magnetic  body  to  be  surrounded 
by  such  currents,  which,  however,  in  the  natural  state  of  the  body  mu- 
tually neutralized  each  other,  on  account  of  their  confused '  grouping. 
The  act  of  magnetization  he  supposed  to  consist  in  setting  these  molecu- 
lar currents  parallel  to  each  other ;  and,  starting  from  this  principle,  he 
reduced  all  the  phenomena  of  magnetism  to  the  mutual  action  of  electric 
currents. 

"  If  we  reflect  upon  the  experiments  recorded  in  the  foregoing  pages 
from  first  to  last,  we  can  hardly  fail  to  be  convinced  that  diamagnetic 
bodies  operated  on  by  magnetic  forces  possess  a  polarity  "  the  same  in 
kind  as,  but  the  reverse  in  direction  of  that  acquired  by  magnetic  bodies." 
But,  if  this  be  the  case,  how  are  we  to  conceive  the  physical  mechanism 
of  this  polarity  ?  According  to  Coulomb's  and  Poisson's  theory,  the  act 
of  magnetization  consists  in  the  decomposition  of  a  neutral  magnetic 
fluid ;  the  north  pole  of  a  magnet,  for  example,  possesses  an  attraction 
for  the  south  fluid  of  a  piece  of  soft  iron  submitted  to  its  influence,  draws 
the  said  fluid  toward  it,  and  with  it  the  material  particles  with  which  the 
fluid  is  associated.  To  account  for  diamagnetic  phenomena  this  theory 
seems  to  fail  altogether ;  according  to  it,  indeed,  the  oft-used  phrase,  "  a 
north  pole  exciting  a  north  pole,  and  a  south  pole  a  south  pole,"  involves 
a  contradiction.  For  if  the  north  fluid  be  supposed  to  be  attracted  tow- 
ard the  influencing  north  pole,  it  is  absurd  to  suppose  that  its  presence 
there  could  produce  repulsion.  The  theory  of  Ampere  is  equally  at  a  loss 
to  explain  diamagnetic  action ;  for  if  we  suppose  the  particles  of  bismuth 
surrounded  by  molecular  currents,  then,  according  to  all  that  is  known 
of  electro-dynamic  laws,  these  currents  would  set  themselves  parallel  to, 
and  in  the  same  direction  as  those  of  the  magnet,  and  hence  attraction, 
and  not  repulsion,  would  be  the  result.  The  fact,  however,  of  this  not 


380  FRAGMENTS  OF  SCIENCE. 

being  the  case  proves  that  these  molecular  currents  are  not  the  mechan- 
ism by  which  diamagnetic  induction  is  effected.  The  consciousness  of 
this,  I  doubt  not,  drove  M.  Weber  to  the  assumption  that  the  phenomena 
of  diamagnetism  are  produced  by  molecular  currents,  not  directed,  but 
actually  excited  in  the  bismuth  by  the  magnet.  Such  induced  currents 
would,  according  to  known  laws,  have  a  direction  opposed  to  those  of  the 
inducing  magnet,  and  hence  would  produce  the  phenomena  of  repulsion. 
To  carry  out  the  assumption  here  made,  M.  Weber  is  obliged  to  suppose 
that  the  molecules  of  diamagnetic  bodies  are  surrounded  by  channels,  in 
which  the  induced  molecular  currents,  once  excited,  continue  to  flow 
without  resistance." — DiG.magndis.rn  and  Magnc-cry&tallic  Action,  pp.  136, 
137. 


XIV. 
SHORTER  ARTICLES. 


SLATES.— DEATH   BY  LIGHTNING.— SCIENCE   AND   SPIRITS.- 
VITALITY.— ADDITIONAL  REMARKS  ON  MIRACLES. 


SLATES. 

(Part  of  a  Lecture  delivered  in  the  Royal  Institution  of  Great  Britain, 
June  6,  1856.) 

WHEN  the  student  of  physical  science  has  to  investigate 
the  character  of  any  natural  force,  his  first  care  must  be  to 
purify  it  from  the  mixture  of  other  forces,  and  thus  study 
its  simple  action.  If,  for  example,  he  wishes  to  know  how 
a  mass  of  liquid  would  shape  itself,  if  at  liberty  to  follow 
the  bent  of  its  own  molecular  forces,  he  must  see  that  these 
forces  have  free  and  undisturbed  exercise.  We  might,  per- 
haps, refer  him  to  the  dew-drop  for  a  solution  of  the  ques- 
tion ;  but  here  we  have  to  do,  not  only  with  the  action  of 
the  molecules  of  the  liquid  upon  each  other,  but  also  with 
the  action  of  gravity  upon  the  mass,  which  pulls  the  drop 
downward  and  elongates  it.  If  he  would  examine  the 
problem  in  its  purity,  he  must  do  as  Plateau  has  done,  de- 
tach the  liquid  mass  from  the  action  of  gravity ;  he  would 
then  find  the  shape  to  be  a  perfect  sphere.  Natural  pro- 
cesses come  to  us  in  a  mixed  manner,  and  to  the  unin- 
structed  mind  are  a  mass  of  unintelligible  confusion.  Sup- 
pose half  a  dozen  of  the  best  musical  performers  to  be  placed 
in  the  same  room,  each  playing  his  own  instrument  to  per- 
fection, but  no  two  playing  the  same  tune ;  though  each  in- 
dividual instrument  might  be  a  source  of  perfect  music,  still 
the  mixture  of  all  would  produce  mere  noise.  Thus  it  is 
with  the  processes  of  Nature.  Here  mechanical  and  mo- 
lecular laws  intermingle  and  create  apparent  confusion. 
Their  mixture  constitutes  what  may  be  called  the  noise  of 


384  FRAGMENTS  OF  SCIENCE. 

natural  laws,  and  it  is  the  vocation  of  the  man  of  science  to 
resolve  this  noise  into  its  components,  and  thus  to  detect 
the  "  music  "  in  which  the  foundations  of  Nature  are  laid. 

The  necessity  of  this  detachment  of  one  force  from  all 
other  forces  is  nowhere  more  strikingly  exhibited  than  in  the 
phenomena  of  crystallization.  Here,  for  example,  is  a  so- 
lution of  common  sulphate  of  soda  or  Glauber  salt.  Look- 
ing into  it  mentally,  we  see  the  molecules  of  that  liquid, 
like  disciplined  squadrons  under  a  governing  eye,  arranging 
themselves  into  battalions,  gathering  round  distinct  centres, 
and  forming  themselves  into  solid  masses,  which  after  a  time 
assume  the  visible  shape  of  the  crystal  now  held  in  my  hand. 
I  may,  like  an  ignorant  meddler  wishing  to  hasten  matters, 
introduce  confusion  into  this  order.  This  may  be  done  by 
plunging  a  glass  rod  into  the  vessel ;  the  consequent  action 
is  not  the  pure  expression  of  the  crystalline  forces ;  the 
molecules  rush  together  with  the  confusion  of  an  unorgan- 
ized mob,  and  not  -with  the  steady  accuracy  of  a  disciplined 
host.  In  this  mass  of  bismuth  also  we  have  an  example  of 
confused  crystallization ;  but  in  the  crucible  behind  me  a 
slower  process  is  going  on :  here  there  is  an  architect  at 
work  "  who  makes  no  chips,  no  din,"  and  who  is  now  build- 
ing the  particles  into  crystals,  similar  in  shape  and  structure 
to  those  beautiful  masses  which  we  see  upon  the  table.  By 
permitting  alum  to  crystallize  in  this  slow  way,  we  obtain 
these  perfect  octahedrons ;  by  allowing  carbonate  of  lime 
to  crystalize,  Nature  produces  these  beautiful  rhomboids ; 
when  silica  crystallizes,  we  have  formed  these  hexagonal 
prisms  capped  at  the  ends  by  pyramids ;  by  allowing  salt- 
petre to  crystallize  we  have  these  prismatic  masses,  and 
when  carbon  crystallizes,  we  have  the  diamond.  If  we  wish 
to  obtain  a  perfect  crystal,  we  must  allow  the  molecular 
forces  free  play :  if  the  crystallizing  mass  be  permitted  to 
rest  upon  a  surface  it  will  be  flattened,  and  to  prevent  this 
a  small  crystal  must  be  so  suspended  as  to  be  surrounded 


SLATES.  385 

on  all  sides  by  the  liquid,  or,  if  it  rest  upon  the  surface,  it 
must  be  turned  daily  so  as  to  present  all  its  faces  in  succes- 
sion to  the  working  builder. 

In  building  up  crystals  these  little  atomic  bricks  often 
arrange  themselves  into  layers  which  are  perfectly  parallel 
to  each  other,  and  which  can  be  separated  by  mechanical 
means ;  this  is  called  the  cleavage  of  the  crystal.  The  crys- 
tal of  sugar  I  hold  in  my  hand  thus  far  escaped  the  solvent 
and  abrading  forces  which  sooner  or  later  determine  the 
fate  of  sugar-candy.  I  readily  discover  that  it  cleaves  with 
peculiar  facility  in  one  direction.  Again,  I  lay  my  knife 
upon  this  piece  of  rock-salt,  and  with  a  blow  cleave  it  in 
one  direction.  Laying  the  knife  at  right  angles  to  its 
former  position,  the  crystal  cleaves  again;  and  finally, 
placing  the  knife  at  right  angles  to  the  two  former  positions, 
we  find  a  third  cleavage.  Rock-salt  cleaves  in  three  di- 
rections, and  the  resulting  solid  is  this  perfect  cube,  which 
may  be  broken  up  into  any  number  of  smaller  cubes.  Ice- 
land spar  also  cleaves  in  three  directions,  not  at  right  angles, 
but  oblique  to  each  other,  the  resulting  solid  being  a  rhom- 
boid. In  each  of  these  cases  the  mass  cleaves  with  equal 
facility  in  all  three  directions.  For  the  sake  of  complete- 
ness I  may  say  that  many  crystals  cleave  with  unequal  fa- 
cility in  different  directions:  heavy  spar  presents  an  ex- 
ample of  this  kind  of  cleavage. 

Turn  we  now  to  the  consideration  of  some  other  phe- 
nomena to  which  the  term  cleavage  may  be  applied.  Beech, 
deal,  and  other  woods,  cleave  with  facility  along  the  fibre, 
and  this  cleavage  is  most  perfect  when  the  edge  of  the  axe 
is  laid  across  the  rings  which  mark  the  growth  of  the  tree. 
If  you  look  at  this  bundle  of  hay  severed  from  a  rick,  you 
will  see  a  sort  of  cleavage  in  it  also ;  the  stalks  lie  in  paral- 
lel planes,  and  only  a  small  force  is  required  to  separate 
them  laterally.  But  we  cannot  regard  the  cleavage  of  the 
tree  as  the  same  in  character  as  that  of  the  hay-rick.  In 
17 


386  FRAGMENTS  OF  SCIENCE. 

the  one  case  it  is  the  molecules  arranging  themselves  ac- 
cording to  organic  laws  which  produce  a  cleavable  struct- 
ure, in  the  other  case  the  easy  separation  in  one  direction 
is  due  to  the  mechanical  arrangement  of  the  coarse  sensible 
masses  of  the  stalks  of  hay. 

This  sand-stone  rock  was  once  a  powder,  more  or  less 
coarse,  held  in  mechanical  suspension  by  water.  The  pow- 
der was  composed  of  two  distinct  parts,  fine  grains  of  sand 
and  small  plates  of  mica.  Imagine  a  wide  strand  covered  by 
a  tide,  or  an  estuary  with  water  which  holds  such  powder  in 
suspension  :  how  will  it  sink  ?  The  rounded  grains  of  sand 
will  reach  the  bottom  first,  because  they  encounter  least  re- 
sistance, the  mica  afterward,  and  when  the  tide  recedes  we 
have  the  little  plates  shining  like  spangles  upon  the  surface 
of  the  sand.  Each  successive  tide  brings  its  charge  of 
mixed  powder,  deposits  its  duplex  layer  day  after  day,  and 
finally  masses  of  immense  thickness  are  piled  up,  which  by 
preserving  the  alternations  of  sand  and  mica  tell  the  tale 
of  their  formation.  Take  the  sand  and  mica,  and  mix  them 
together  in  water,  and  allow  them  to  subside ;  they  will  ar- 
range themselves  in  the  manner  indicated,  and  by  repeating 
the  process  you  can  actually  build  up  a  mass  which  shall  be 
the  exact  counterpart  of  that  presented  by  Nature.  Now  this 
structure  cleaves  with  readiness  along  the  planes  in  which 
the  particles  of  mica  are  strewn.  Specimens  of  such  a  rock 
sent  to  me  from  Halifax,  and  other  masses  from  the  quarries 
of  Over  Darwen  in  Lancashire,  are  here  before  you.  With 
a  hammer  and  chisel  I  can  cleave  them  into  flags ;  indeed, 
these  flags  are  employed  for  roofing  purposes  in  the  districts 
from  which  the  specimens  have  come,  and  receive  the  name 
of  "  slate-stone."  But  you  will  discern  without  a  word 
from  me,  that  this  cleavage  is  not  a  crystalline  cleavage 
any  more  than  that  of  a  hay-rick.  It  is  molar,  not  molec- 
ular. 

This,  so  far  as  I  am  aware  of,  has  never  been  imagined, 


SLATES.  387 

and  it  has  been  agreed  among  geologists  not  to  call  such 
splitting  as  this  cleavage  at  all,  but  to  restrict  the  term  to 
a  phenomenon  of  a  totally  different  character. 

Those  who  have  visited  the  slate-quarries  of  Cumberland 
and  North  Wales  will  have  witnessed  the  phenomenon  to 
which  I  refer.  We  have  long  drawn  our  supply  of  roofing- 
slates  from  such  quarries ;  school-boys  ciphered  on  these 
slates,  they  were  used  for  tombstones  in  church-yards,  and 
for  billiard-tables  in  the  metropolis ;  but  not  until  a  com- 
paratively late  period  did  men  begin  to  inquire  how  their 
wonderful  structure  was  produced.  What  is  the  agency 
which  enables  us  to  split  Honister  Crag,  or  the  cliffs  of 
Snowdon,  into  laminae  from  crown  to  base  ?  This  question 
is  at  the  present  moment  one  of  the  great  difficulties  of 
geologists,  and  occupies  their  attention  perhaps  more  than 
any  other.  You  may  wonder  at  this.  Looking  into  the 
quarry  of  Penrhyn,  you  may  be  disposed  to  offer  the  ex- 
planation I  heard  given  two  years  ago.  "  These  planes  of 
cleavage,"  said  a  friend  who  stood  beside  me  on  the  quarry's 
edge,  "  are  the  planes  of  stratification  which  have  been 
lifted  by  some  convulsion  into  an  almost  vertical  position." 
But  this  was  a  mistake,  and  indeed  here  lies  the  grand  diffi- 
culty of  the  problem.  The  planes  of  cleavage  stand  in  most 
cases  at  a  high  angle  to  the  bedding.  Thanks  to  Sir  Roder- 
ick Murchison,  I  am  able  to  place  the  proof  of  this  before 
you.  Here  is  a  specimen  of  slate  in  which  both  the  planes 
of  cleavage  and  of  bedding  are  distinctly  marked,  one  of 
them  making  a  large  angle  with  the  other.  This  is  com- 
mon. The  cleavage  of  slates,  then,  is  not  a  question  of 
stratification  ;  what,  then,  is  its  cause  ? 

In  an  able  and  elaborate  essay  published  in  1835,  Pro- 
fessor Sedgwick  proposed  the  theory  that  cleavage  is  due 
to  the  action  of  crystalline  or  polar  forces  subsequent  to  the 
consolidation  of  the  rock.  "  We  may  affirm,"  he  says,  "  that 
no  retreat  of  the  parts,  no  contraction  of  dimensions  in  pass- 


388  FRAGMENTS  OF  SCIENCE. 

ing  to  a  solid  state,  can  explain  such  .phenomena.  They 
appear  to  me  only  resolvable  on  the  supposition  that  crystal- 
line or  polar  forces  acted  upon  the  whole  mass  simultane- 
ously in  one  direction  and  with  adequate  force."  And  again, 
in  another  place  :  "  Crystalline  forces  have  rearranged  whole 
mountain-masses,  producing  a  beautiful  crystalline  cleavage, 
passing  alike  through  all  the  strata."  1  The  utterance  of 
such  a  man  struck  deep,  as  it  ought  to  do,  into  the  minds 
of  geologists,  arid  at  the  present  day  there  are  few  who  do 
not  entertain  this  view  either  in  whole  or  in  part.2  The 
boldness  of  the  theory,  indeed,  has,  in  some  cases,  caused 
speculation  to  run  riot,  and  we  have  books  published  on  the 
action  cf  polar  forces  and  geologic  magnetism,  which  rather 
astonish  those  who  know  something  about  the  subject.  Ac- 
cording to  this  theory,  whole  districts  of  North  Wales  and 
Cumberland,  mountains  included,  are  neither  more  nor  less 
than  the  parts  of  a  gigantic  crystal.  These  masses  of  slate 
were  originally  fine  mud,  composed  of  the  broken  and 
abraded  particles  of  older  rocks.  They  contain  silica,  alu- 
mina, potash,  soda,  and  mica,  mixed  mechanically  together. 
In  the  course  of  ages  the  mixture  became  consolidated,  and 
the  theory  before  us  assumes  that  a  process  of  crystalliza- 
tion afterward  rearranged  the  particles  and  developed  in  it 
a  single  plane  of  cleavage.  Though  a  bold,  and  I  think  in- 
admissible, stretch  of  analogies,  this  hypothesis  has  done 

1  Transactions  of  the  Geological  Society,  ser.  ii.  vol.  iii.  p.  477. 

2  In  a  letter  to  Sir  Charles  Lyell,  dated  from  the  Cape  of  Good  Hope 
February  20,  1836,  Sir  John  Herschel  writes  as  follows  :  "  If  rocks  have 
been  so  heated  as  to  allow  of  a  commencement  of  crystallization,  that  is 
to  say,  if  they  have  been  heated  to  a  point  at  which  the  particles  can  be- 
gin to  move  among  themselves,  or  at  least  on  their  own  axes,  some  gen- 
eral law  must  then  determine  the  position  in  which  these  particles  will 
rest  on  cooling.     Probably  that  position  will  have  some  relation  to  the 
direction  in  which  the  heat  escapes.     Now,  when  all  or  a  majority  of  par- 
ticles of  the  same  nature  have  a  general  tendency  to  one  position,  that 
must  of  course  determine  a  cleavage  plane." 


SLATES.  389 

good  service.  Right  or  wrong,  a  thoughtfully  -  uttered 
theory  has  a  dynamic  pow.er  which  operates  against  intel- 
lectual stagnation;  and  even  by  provoking  opposition  is 
eventually  of  service  to  the  cause  of  truth.  It  would,  how- 
ever, have  been  remarkable  if,  among  the  ranks  of  geolo- 
gists themselves,  men  were  not  found  to  seek  an  explana- 
tion of  slate-cleavage  involving  a  less  hardy  assumption. 

The  first  step  in  an  inquiry  of  this  kind  is  to  seek  facts. 
This  has  been  done,  and  the  labors  of  Daniel  Sharpe  (the 
late  President  of  the  Geological  Society,  who,  to  the  loss 
of  science  and  the  sorrow  of  all  who  knew  him,  has  so  sud- 
denly been  taken  away  from  us),  Mr.  Henry  Clifton  Sorby, 
and  others,  have  furnished  us  with  a  body  of  facts  associated 
with  slaty  cleavage,  and  having  a  most  important  bearing 
upon  the  question. 

Fossil  shells  are  found  in  these  slate-rocks.  I  have  here 
several  specimens  of  such  shells  in  the  actual  rock,  and  oc- 
cupying various  positions  in  regard  to  the  cleavage  planes. 
They  are  squeezed,  distorted,  and  crushed ;  in  all  cases  the 
distortion  leads  to  the  inference  that  the  rock  which  con- 
tains these  shells  has  been  subjected  to  enormous  pressure 
in  a  direction  at  right  angles  to  the  planes  of  cleavage. 
The  shells  are  all  flattened  and  spread  out  in  these  planes. 
Compare  this  fossil  trilobite  of  normal  proportions  with 
these  others  which  have  suffered  distortion.  Some  have 
lain  across,  some  along,  and  some  oblique  to  the  cleavage  of 
the  slate  in  which  they  are  found ;  but  in  all  cases  the  dis- 
tortion is  such  as  required  for  its  production  a  compressing 
force  acting  at  right  angles  to  the  planes  of  cleavage.  As 
the  trilobites  lay  in  the  mud,  the  jaws  of  a  gigantic  vice  ap- 
pear to  have  closed  upon  them  and  squeezed  them  into  the 
shapes  you  see. 

We  sometimes  find  a  thin  layer  of  coarse,  gritty  mate- 
rial, between  two  layers  of  finer  rock,  through  which  and 
across  the  gritty  layer  pass  the  planes  of  lamination.  The 


390  FRAGMENTS  OF  SCIENCE. 

coarse  layer  is  found  bent  by  the  pressure  into  sinuosities 
like  a  contorted  ribbon.  Mr.  Sorby  has  described  a  striking 
case  of  this  kind.  This  crumpling  can  be  experimentally 
imitated ;  the  amount  of  compression  might,  moreover,  be 
rough tly  estimated  by  supposing  the  contorted  bed  to  be 
stretched  out,  its  length  measured  and  compared  with  the 
shorter  distance  into  which  it  has  been  squeezed.  We  find 
in  this  way  that  the  yielding  of  the  mass  has  been  consider- 
able. 

Let  me  now  direct  your  attention  to  another  proof  of 
pressure ;  you  see  the  varying  colors  which  indicate  the 
bedding  on  this  mass  of  slate.  The  dark  portion  is  gritty, 
being  composed  of  comparatively  coarse  particles,  which, 
owing  to  their  size,  shape,  and  gravity,  sink  first  and  con- 
stitute the  bottom  of  each  layer.  Gradually,  from  bottom 
to  top  the  coarseness  diminishes,,  and  near  the  upper  sur- 
face we  have  a  layer  of  exceedingly  fine  mud.  It  is  the 
mud  thus  consolidated  from  which  are  derived  the  German 
razor-stones,  so  much  prized  for  the  sharpening  of  surgical 
instruments.  When  a  bed  is  thin,  the  fine  white  mud  is 
permitted  to  rest  upon  a  slab  of  the  coarser  slate  in  contact 
with  it :  when  the  bed  is  thick  it  is  cut  into  slices,  which 
are  cemented  to  pieces  of  ordinary  slate,  and  thus  rendered 
stronger.  The  mud  thus  deposited  is,  as  might  be  ex- 
pected, often  rolled  up  into  nodular  masses,  carried  for- 
ward, and  deposited  among  coarser  material  by  the  rivers 
from  which  the  slate-mud  has  subsided.  Here  are  such 
nodules  enclosed  in  sandstone.  Everybody,  moreover,  who 
has  ciphered  upon  a  school-slate  must  remember  the  whitish- 
green  spots  which  sometimes  dotted  the  surface  of  the 
slate,  and  over  which  the  pencil  usually  slid  as  if  the  spots 
were  greasy.  Now  these  spots  are  composed  of  the  finer 
mud,  and  they  could  not,  on  account  of  their  fineness,  bite 
the  pencil  like  the  surrounding  gritty  portions  of  the  slate. 
Here  is  a  beautiful  example  of  these  spots :  you  observe 


SLATES.  391 

them  on  the  cleavage  surface  in  broad  round  patches.  But 
turn  the  slate  edgeways  and  the  section  of  each  nodule  is 
seen  to  be  a  sharp  oval,  with  its  longer  axis  parallel  to  the 
cleavage.  This  instructive  fact  has  been  adduced  by  Mr. 
Sorby.  I  have  made  excursions  to  the  quarries  of  Wales 
and  Cumberland,  and  to  many  of  the  slate-yards  of  London, 
and  found  the  fact  general.  Thus  we  elevate  a  common 
experience  of  our  boyhood  into  evidence  of  the  highest 
significance  as  regards  a  most  important  geological  problem. 
From  the  magnetic  deportment  of  these  slates,  I  was  led  to 
infer  that  these  spots  contain  a  less  amount  of  iron  than  the 
surrounding  dark  slate.  An  analysis  was  made  for  me  by 
Mr.  Hambly  in  the  laboratory  of  Dr.  Percy  at  the  School  of 
Mines,  with  the  following  result : 

ANALYSIS  OF  SLATE. 
Dark  Slate,  two  Analyses. 

1.  Percentage  of  iron 5.85 

2.  "  " 6.13 

Mean 5.99 

WhitisJi-green  Slate. 

1.  Percentage  of  iron 3.24 

2.  "  "  3.12 


According  to  these  analyses,  the  quantity  of  iron  in  the 
dark  slate  immediately  adjacent  to  the  greenish  spot  is 
nearly  double  the  quantity  contained  in  the  spot  itself. 
This  is  about  the  proportion  which  the  magnetic  experi- 
ments suggested. 

Let  me  now  remind  you  that  the  facts  brought  before 
you  are  typical — each  is  the  representative  of  a  class.  We 
have  seen  shells  crushed ;  the  unhappy  trilobites  squeezed, 
beds  contorted,  nodules  of  greenish  marl  flattened ;  and  all 
these  sources  of  independent  testimony  point  to  one  and 
the  same  conclusion,  namely,  that  slate-rocks  have  been 


392  FRAGMENTS  OF  SCIENCE. 

subjected  to  enormous  pressure  in  a  direction  at  right  angles 
to  the  planes  of  cleavage. 

In  reference  to  Mr.  Sorby's  contorted  bed,  I  have  said 
that  by  supposing  it  to  be  stretched  out  and  its  length 
measured,  it  would  give  us  an  idea  of  the  amount  of  yield- 
ing of  the  mass  above  and  below  the  bed.  Such  a  measure- 
ment, however,  would  not  give  the  exact  amount  of  yielding. 
I  hold  in  my  hand  a  specimen  of  slate  with  its  bedding 
marked  upon  it ;  the  lower  portions  of  each  layer  being 
composed  of  a  comparatively  coarse  gritty  material  some- 
thing like  what  you  may  suppose  the  contorted  bed  to  be 
composed  of.  Now,  in  crossing  these  gritty  portions,  the 
cleavage  turns,  as  if  tending  to  cross  the  bedding  at  an- 
other angle.  When  the  pressure  began  to  act,  the  inter- 
mediate bed,  which  is  not  entirely  unyielding,  suffered 
longitudinal  pressure ;  as  it  bent,  the  pressure  became  grad- 
ually more  lateral,  and  the  direction  of  its  cleavage  is  ex- 
actly such  as  you  would  infer  from  an  action  of  this  kind — it 
is  neither  quite  across  the  bed  nor  yet  in  the  same  direction 
as  the  cleavage  of  the  slate  above  and  below  it,  but  inter- 
mediate between  both.  Supposing  the  cleavage  to  be  at 
right  angles  to  the  pressure,  this  is  the  direction  which  it 
ought  to  take  across  these  more  unyielding  strata. 

Thus  we  have  established  the  concurrence  of  the  phe- 
nomena of  cleavage  and  pressure — that  they  accompany 
each  other ;  but  the  question  still  remains,  Is  the  pressure 
sufficient  to  account  for  the  cleavage  ?  A  single  geologist, 
as  far  as  I  am  aware,  answers  boldly  in  the  affirmative. 
This  geologist  is  Sorby,  who  has  attacked  the  question  in 
the  true  spirit  of  a  physical  investigator.  Call  to  mind  the 
cleavage  of  the  flags  of  Halifax  and  Over  Darwen,  which  is 
caused  by  the  interposition  of  layers  of  mica  between  the 
gritty  strata.  Mr.  Sorby  finds  plates  of  mica  to  be  also  a 
constituent  of  slate-rock.  He  asks  himself,  what  will  be 
the  effect  of  pressure  upon  a  mass  containing  such  plates 


SLATES.  393 

confusedly  mixed  up  in  it  ?  It  will  be,  he  argues,  and  he 
argues  rightly,  to  place  the  plates  with  their  flat  surfaces 
more  or  less  perpendicular  to  the  direction  in  which  the 
pressure  is  exerted.  He  takes  scales  of  the  oxide  of  iron, 
mixes  them  with  a  fine  powder,  and  on  squeezing  the  mass 
finds  that  the  tendency  of  the  scales  is  to  set  themselves  at 
right  angles  to  the  line  of  pressure.  Along  the  planes  of 
weakness  produced  by  the  scales  the  mass  cleaves. 

By  tests  of  a  different  character  from  those  applied  by 
Mr.  Sorby,  it  might  be  shown  how  true  his  conclusion  is, 
that  the  effect  of  pressure  on  elongated  particles  or  plates 
will  be  such  as  he  describes  it.  But  while  the  scales  must 
be  regarded  as  a  true  cause,  I  should  not  ascribe  to  them  a 
large  share  in  the  production  of  the  cleavage.  I  believe 
that,  even  if  the  plates  of  mica  were  wholly  absent,  the 
cleavage  of  slate-rocks  would  be  much  the  same  as  it  is  at 
present. 

Here  is  a  mass  of  pure  white  wax :  it  contains  no  mica 
particles,  no  scales  of  iron,  nor  any  thing  analogous  to  them. 
Here  is  the  self-same  substance  submitted  to  pressure.  I 
would  invite  the  attention  of  the  eminent  geologists  now 
before  me  to  the  structure  of  this  wax.  No  slate  ever  ex- 
hibited so  clean  a  cleavage ;  it  splits  into  laminae  of  sur- 
passing tenuity,  and  proves  at  a  single  stroke  that  pressure 
is  sufficient  to  produce  cleavage,  and  that  this  cleavage  is 
independent  of  intermixed  plates  or  scales.  I  have  pur- 
posely mixed  this  wax  with  elongated  particles,  and  am 
unable  to  say  at  the  present  moment  that  the  cleavage  is 
sensibly  affected  by  their  presence — if  any  thing,  I  should 
say  they  rather  impair  its  fineness  and  clearness  than  pro- 
mote it. 

The  finer  the  slate  is  the  more  perfect  will  be  the  re- 
semblance of  its  cleavage  to  that  of  the  wax.  Compare 
the  surface  of  the  wax  with  the  surface  of  this  slate  from 
Borrodale  in  Cumberland.  You  have  precisely  the  same 


394  FRAGMENTS  OF  SCIENCE. 

features  in  both :  you  see  flakes  clinging  to  the  surfaces  of 
each,  which  have  been  partially  torn  away  in  cleaving. 
Let  any  close  observer  compare  these  two  effects,  he  will, 
I  am  persuaded,  be  led  to  the  conclusion  that  they  are  the 
product  of  a  common  cause.1 

But  you  will  ask  me  how,  according  to  my  view,  does 
pressure  produce  this  remarkable  result.  This  may  be 
stated  in  a  very  few  words : 

There  is  no  such  thing  in  Nature  as  a  body  of  perfectly 
homogeneous  structure.  I  breakr  this  clay  which  seems  so 
uniform,  and  find  that  the  fracture  presents  to  my  eyes  in- 
numerable surfaces  along  which  it  has  given  way,  and  it 
has  yielded  along  those  surfaces  because  in  them  the  cohe- 
sion of  the  mass  is  less  than  elsewhere.  I  break  this  mar- 
ble, and  even  this  wax,  and  observe  the  same  result ;  look 
at  the  mud  at  the  bottom  of  a  dried  pond ;  look  to  some  of 
the  ungra veiled  walks  in  Kensington  Gardens  on  drying  af- 
ter rain — they  are  cracked  and  split,  and,  other  circumstances 
being  equal,  they  crack  and  split  where  the  cohesion  is  least. 
Take  then  a  mass  of  partially  consolidated  mud.  Such  a 
mass  is  divided  and  subdivided  by  interior  surfaces  along 
which  the  cohesion  is  comparatively  small.  Penetrate  the 
mass  in  idea,  and  you  will  see  it  composed  of  numberless 
irregular  polyhedra  bounded  by  surfaces  of  weak  cohesion. 
Imagine  such  a  mass  subjected  to  pressure — it  yields  and 
spreads  out  in  the  direction  of  least  resistance  ; a  the  little 

1  I  have  usually  softened  the  wax  by  warming  it,  kneaded  it  with  the 
fingers,  and  pressed-  it  between  thick  plates  of  glass  previously  wetted. 
At  the  ordinary  summer  temperature  the  pressed  wax  is  soft,  and  tears 
rather  than  cleaves  ;  on  this  account,  I  cool  my  compressed  specimens  in 
a  mixture  of  pounded  ice  and  salt,  and  when  thus  cooled  they  split  beau- 
tifully. 

2  It  is  scarcely  necessary  to  say  that,  if  the  mass  were  squeezed  equal- 
ly in  all  directions,  no  laminated  structure  could  be  produced  ;  it  must 
have  room  to  yield  in  a  lateral  direction.     Mr.  Warren  De  la  Rue  informs 
me  that  he  once  wished  to  obtain  white-lead  in  a  fine  granular  state,  and 


SLATES.  395 

polyhedra  become  converted  into  laminae,  separated  from 
each  other  by  surfaces  of  weak  cohesion,  and  the  infallible 
result  will  be  a  tendency  to  cleave  at  right  angles  to  the 
line  of  pressure. 

Further,  a  mass  of  dried  mud  is  full  of  cavities  and  fis- 
sures. If  you  break  dried  pipe-clay  you  see  them  in  great 
numbers,  and  there  are  multitudes  of  them  so  small  that  you 
cannot  see  them.  A  flattening  of  these  cavities  must  take 
place  in  squeezed  mud,  and  this  must  to  some  extent  facili- 
tate the  cleavage  of  the  mass  in  the  direction  indicated. 

Although  the  time  at  my  disposal  has  not  permitted  me 
duly  to  develop  these  thoughts,  yet  for  the  last  twelve 
months  the  subject  has  presented  itself  to  me  almost  daily 
under  one  aspect  or  another.  I  have  never  eaten  a  biscuit 
during  this  period  without  remarking  the  cleavage  devel- 
oped by  the  rolling-pin.  You  have  only  to  break  a  biscuit 
across,  and  to  look  at  the  fracture,  to  see  the  laminated 
structure.  We  have  here  the  means  of  pushing  the  anal- 
ogy further.  I  invite  you  to  compare  the  structure  of  this 
slate,  which  was  subjected  to  a  high  temperature  during 
the  conflagration  of  Mr.  Scott  Russell's  premises,  with  that 
of  a  biscuit.  Air  or  vapor  within  the  slate  has  caused  it 
to  swell,  and  the  mechanical  structure  it  reveals  is  precisely 
that  of  a  biscuit.  During  these  inquiries  I  have  received 
much  instruction  in  the  manufacture  of  puff-paste.  Here 
is  some  such  paste  baked  under  my  own  superintendence. 
The  cleavage  of  our  hills  is  accidental  cleavage,  but  this  is 
cleavage  with  intention.  The  volition  of  the  pastry-cook 
has  entered  into  its  formation.  It  has  been  his  aim  to  pre- 
serve a  series  of  surfaces  of  structural  weakness,  along 
which  the  dough  divides  into  layers.  Puff-paste  in  prepa- 

to  accomplish  this  he  first  compressed  it.  The  mould  was  conical,  and 
permitted  the  lead  to  spread  out  a  little  laterally.  The  lamination  was 
as  perfect  as  that  of  slate,  and  it  quite  defeated  him  in  his  effort  to  ob- 
tain a  granular  powder. 


396  FRAGMENTS  OF  SCIENCE. 

ration  must  not  be  handled  too  much ;  it  ought,  moreover, 
to  be  rolled  on  a  cold  slab,  to  prevent  the 'butter  from  melt- 
ing, and  diffusing  itself,  thus  rendering  the  paste  more  ho- 
mogeneous and  less  liable  to  split.  Puff-paste  is,  then, 
'  simply  an  exaggerated  case  of  slaty  cleavage. 

The  principle  which  I  have  enunciated  is  so  simple  as 
to  be  almost  trivial ;  nevertheless,  it  embraces  not  only  the 
cases  mentioned,  but,  if  time  permitted,  it  might  be  shown 
you  that  the  principle  has  a  much  wider  range  of  applica- 
tion. When  iron  is  taken  from  the  puddling-furnace  it  is 
more  or  less  spongy,  an  aggregate  in  fact  of  small  nod- 
ules :  it  is  at  a  welding  heat,  and  at  this  temperature  is 
submitted  to  the  process  of  rolling.  Bright,  smooth  bars 
are  the  result.  But,  notwithstanding  the  high  heat,  the 
nodules  do  not  perfectly  blend  together.  The  process  of 
rolling  draws  them  into  fibres.  Here  is  a  mass  acted  upon 
by  dilute  sulphuric  acid,  which  exhibits  in  a  striking  man- 
ner this  fibrous  structure.  The  experiment  was  made  by 
my  friend  Dr.  Percy,  without  any  reference  to  the  question 
of  cleavage. 

Break  a  piece  of  ordinary  iron,  and  you  have  a  granular 
fracture ;  beat  the  iron,  you  elongate  these  granules,  and 
finally  render  the  mass  fibrous.  Here  are  pieces  of  rails 
along  which  the  wheels  of  locomotives  have  slidden  ;  the 
granules  have  yielded  and  become  plates.  They  exfoliate 
or  come  off  in  leaves ;  all  these  effects  belong,  I  believe, 
to  the  great  class  of  phenomena  of  which  slaty  cleavage 
forms  the  most  prominent  example.1 

[I  would  now  lay  more  stress  on  the  lateral  yielding, 
referred  to  in  the  note  at  the  bottom  of  page  394,  accompa- 
nied as  it  is  by  tangential  sliding,  than  I  was  prepared  to 
do  when  this  lecture  was  given.  This  sliding  is,  I  think, 
the  principal  cause  of  the  planes  of  weakness  both  in 
pressed  wax  and  slate-rock.  J.  T.  1871.] 

1  For  some  further  observations  on  this  subject  by  Mr.  Sorby  and 
myself,  see  Philosophical  Magazine  for  August,  1856. 


DEATH  BY  LIGHTNING. 

PEOPLE  in  general  imagine,  when  they  think  at  all  about 
the  matter,  that  an  impression  upon  the  nerves — a  blow, 
for  example,  or  the  prick  of  a  pin — is  felt  at  the  moment  it 
is  inflicted.  But  this  is  not  the  case.  The  seat  of  sensa- 
tion is  the  brain,  and  to  it  the  intelligence  of  any  impression 
made  upon  the  nerves  has  to  be  transmitted  before  this 
impression  can  become  manifest  in  consciousness.  The 
transmission,  moreover,  requires  time,  and  the  consequence 
is,  that  a  wound  inflicted  on  a  portion  of  the  body  distant 
from  the  brain  is  more  tardily  appreciated  than  one  inflicted 
adjacent  to  the  brain.  By  an  extremely  ingenious  experi- 
mental arrangement,  Helmholtz  has  determined  the  velocity 
of  this  nervous  transmission,  and  finds  it  to  be  about  one 
hundred  feet  a  second,  or  less  than  one-tenth  of  the  velocity 
of  sound  in  air.  If,  therefore,  a  whale  fifty  feet  long  were 
wounded  in  the  tail,  it  would  not  be  conscious  of  the  injury 
till  half  a  second  after  the  wound  had  been  inflicted.1  But 
this  is  not  the  only  ingredient  in  the  delay.  There  can 
scarcely  be  a  doubt  that  to  every  act  of  consciousness  be- 
longs a  determinate  molecular  arrangement  of  the  brain — 
that  every  thought  or  feeling  has  its  physical  correlative  in 
that  organ;  and  nothing  can  be  more  certain  than  that 
every  physical  change,  whether  molecular  or  mechanical, 
requires  time  for  its  accomplishment.  So  that,  besides  the 

1  A  most  admirable  lecture  on  the  velocity  of  nervous  transmission 
has  been  published  by  Dr.  Du  Bois-Raymond  in  the  Proceedings  of  the 
Royal  Institution  for  1866,  vol.  iv.  p.  575. 


398  FKAGMENTS  OF  SCIENCE. 

interval  of  transmission,  a  still  further  time  is  necessary  for 
the  brain  to  put  itself  in  order — for  its  molecules  to  take 
up  the  motions  or  positions  necessary  to  the  completion  of 
consciousness.  Helmholtz  considers  that  one-tenth  of  a 
second  is  demanded  for  this  purpose.  Thus,  in  the  case  of 
the  whale  above  supposed,  we  have  first  half  a  second  con- 
sumed in  the  transmission  of  the  intelligence  through  the 
sensor  nerves  to  the  head,  one-tenth  of  a  second  consumed 
by  the  brain  in  completing  the  arrangements  necessary  to 
consciousness,  and,  if  the  velocity  of  transmission  through 
the  motor  be  the  same  as  that  through  the  sensor  nerves, 
half  a  second  in  sending  a  command  to  the  tail  to  defend 
itself.  Thus  one  second  and  a  tenth  would  elapse  before 
an  impression  made  upon  its  caudal  nerves  could  be  re- 
sponded to  by  a  whale  fifty  feet  long. 

Now,  it  is  quite  conceivable  that  an  injury  might  be 
inflicted  which  would  render  the  nerves  unfit  to  be  the  con- 
ductors of  the  motion  which  results  in  sensation ;  and  if 
such  a  thing  occurred,  no  matter  how  severe  the  injury 
might  be,  we  should  not  be  conscious  of  it.  Or  it  may 
be  that,  long  before  the  time  required  by  the  brain  to 
complete  the  arrangement  necessary  to  consciousness,  its 
power  of  arrangement  might  be  wholly  suspended.  In 
such  a  case  also,  though  the  injury  might  be  of  a  nature 
to  cause  death,  this  would  occur  without  feeling  of  any 
kind.  Death  in  this  case  would  be  simply  the  sudden 
negation  of  life,  without  any  intervention  of  consciousness 
whatever. 

Doubtless  there  are  many  kinds  of  death  of  this  char- 
acter. The  passage  of  a  musket-bullet  through  the  brain 
is  a  case  in  point ;  and  the  placid  aspect  of  a  man  thus  killed 
is  in  perfect  accordance  with  the  conclusion  which  might  be 
drawn  a  priori  from  the  experiments  of  Helmholtz.  Cases 
of  insensibility,  moreover,  are  not  uncommon  which  do  not 
result  in  death,  and  after  which  the  persons  affected  have 


DEATH  BY  LIGHTNING.  399 

been  able  to  testify  that  no  pain  was  felt  prior  to  the  loss 
of  consciousness. 

The  time  required  for  a  rifle-bullet  to  pass  clean  through 
a  man's  head  may  be  roughly  estimated  at  a  thousandth  of 
a  second.  Here,  therefore,  we  should  have  no  room  for 
sensation,  and  death  would  be  painless.  But  there  are 
other  actions  which  far  transcend  in  rapidity  that  of  the 
rifle-bullet.  A  flash  of  lightning  cleaves  a  cloud,  appearing 
and  disappearing  in  less  than  a  hundred-thousandth  of  a 
second,  and  the  velocity  of  electricity  is  such  as  would  carry 
it  in  a  single  second  over  a  distance  almost  equal  to  that 
which  separates  the  earth  and  moon.  It  is  well  known 
that  a  luminous  impression  once  made  upon  the  retina  en- 
dures for  about  one-sixth  of  a  second,  and  that  this  is  the 
reason  why  we  see  a  ribbon  of  light  when  a  glowing  coal 
is  caused  to  pass  rapidly  through  the  air.  A  body  illumi- 
nated by  an  instantaneous  flash  continues  to  be  seen  for  the 
sixth  of  a  second  after  the  flash  has  become  extinct ;  and 
if  the  body  thus  illuminated  be  in  motion,  it  appears  at 
rest  at  the  place  where  the  flash  falls  upon  it.  The  color- 
top  is  familiar  to  most  of  us.  By  this  instrument  a  disk 
with  differently-colored  sectors  is  caused  to  rotate  rapidly ; 
the  colors  blend  together,  and,  if  they  are  chosen  in  the 
proper  proportions,  when  the  motion  is  sufficiently  rapid 
the  disk  appears  white.  Such  a  top,  rotating  in  a  dark  room 
and  illuminated  by  an  electric  spark,  appears  motionless, 
each  distinct  color  being  clearly  seen.  Professor  Dove  has 
found  that  a  flash  of  lightning  produces  the  same  effect. 
During  a  thunder-storm  he  put  a  color-top  in  exceedingly 
rapid  motion,  and  found  that  every  flash  revealed  the  top 
as  a  motionless  object  with  its  colors  distinct.  If  illuminated 
solely  by  a  flash  of  lightning,  the  motion  of  all  bodies  on 
the  earth's  surface  would,  as  Dove  has  remarked,  appear 
suspended.  A  cannon-ball,  for  example,  would  have  its 
flight  apparently  arrested,  and  would  seem  to  hang  motion- 


400  FRAGMENTS  OF  SCIENCE. 

less  in  space  as  long  as  the  luminous  impression  which  re- 
vealed the  ball  remained  upon  the  eye. 

If,  then,  a  rifle-bullet  move  with  sufficient  rapidity  to 
destroy  life  without  the  interposition  of  sensation,  much 
more  is  a  flash  of  lightning  competent  to  produce  this  effect. 
Accordingly,  we  have  well-authenticated  cases  of  people 
being  struck  senseless  by  lightning  who,  on  recovery,  had 
no  memory  of  pain.  The  following  circumstantial  case  is 
described  by  Hemmer : 

On  June  30,  1788,  a  soldier  in  the  neighborhood  of 
Mannheim,  being  overtaken  by  rain,  placed  himself  under 
a  tree,  beneath  which  a  woman  had  previously  taken 
shelter.  He  looked  upward  to  see  whether  the  branches 
were  thick  enough  to  afford  the  required  protection,  and, 
in  doing  so,  was  struck  by  lightning,  and  fell  senseless  to 
the  earth.  The  woman  at  his  side  experienced  the  shock 
in  her  foot,  but  was  not  struck  down.  Some  hours  after- 
ward the  man  revived,  but  remembered  nothing  about 
what  had  occurred,  save  the  fact  of  his  looking  up  at  the 
branches.  This  was  his  last  act  of  consciousness,  and  he 
passed  from  the  conscious  to  the  unconscious  condition 
without  pain.  The  visible  marks  of  a  lightning-stroke 
are  usually  insignificant :  the  hair  is  sometimes  burnt ; 
slight  wounds  are  observed ;  while,  in  some  instances, 
a  red  streak  marks  the  track  of  the  discharge  over  the 
skin. 

Under  ordinary  circumstances,  the  discharge  from  a 
small  Leyden-jar  is  exceedingly  unpleasant  to  myself. 
Some  time  ago  I  happened  to  stand  in  the  presence  of  a 
numerous  audience,  with  a  battery  of  fifteen  large  Leyden- 
jars  charged  beside  me.  Through  some  awkwardness  on 
my  part,  I  touched  a  wire  leading  from  the  battery,  and 
the  discharge  went  through  my  body.  Life  was  absolutely 
blotted  out  for  a  very  sensible  interval,  without  a  trace  of 
pain.  In  a  second  or  so  consciousness  returned ;  I  saw  my- 


DEATH  BY  LIGHTNING.  401 

self  in  the  presence  of  the  audience  and  apparatus,  and,  by 
the  help  of  these  external  appearances,  immediately  con- 
cluded that  I  had  received  the  battery  discharge.  The  in- 
tellectual consciousness  of  my  position  was  restored  with 
exceeding  rapidity,  but  not  so  the  optical  consciousness. 
To  prevent  the  audience  from  being  alarmed,  I  observed 
that  it  had  often  been  my  desire  to  receive  accidentally 
such  a  shock,  and  that  my  wish  had  at  length  been  fulfilled. 
But  while  making  this  remark,  the  appearance  which  my 
body  presented  to  myself  was  that  of  a  number  of  separate 
pieces.  The  arms,  for  example,  were  detached  from  the 
trunk,  and  seemed  suspended  in  the  air.  In  fact,  memory 
and  the  power  of  reasoning  appeared  to  be  complete  long 
before  the  optic  nerve  was  restored  to  healthy  action.  But 
what  I  wish  chiefly  to  dwell  upon  here  is,  the  absolute  pain- 
lessness  of  the  shock ;  and  there  cannot  be  a  doubt  that,  to 
a  person  struck  dead  by  lightning,  the  passage  from  life  to 
death  occurs  without  consciousness  being  in  the  least  de- 
gree implicated.  It  is  an  abrupt  stoppage  of  sensation, 
unaccompanied  by  a  pang. 
July  8,  1865. 


SCIENCE  AND  SPIRITS. 

THEIR  refusal  to  investigate  "  spiritual  phenomena  "  is 
often  urged  as  a  reproach  to  scientific  men.  I  here  propose 
to  give  a  sketch  of  an  attempt  to  apply  to  the  "  phenom- 
ena "  those  methods  of  inquiry  which  are  found  available 
in  dealing  with  natural  truth. 

Some  time  ago,  when  the  spirits  were  particularly 
active  in  this  country,  a  celebrated  philosopher  was  invited, 
or  rather  entreated,  by  one  of  his  friends  to  meet  and  ques- 
tion them.  He  had,  however,  already  made  their  acquaint- 
ance, and  did  not  wish  to  renew  it.  I  had  not  been  so 
privileged,  and  he  therefore  kindly  arranged  a  transfer  of 
the  invitation  to  me.  The  spirits  themselves  named  the 
time  of  meeting,  and  I  was  conducted  to  the  place  at  the 
day  and  hour  appointed. 

Absolute  unbelief  in  the  facts  was  by  no  means  my  con- 
dition of  mind.  On  the  contrary,  I  thought  it  probable 
that  some  physical  principle,  not  evident  to  the  spiritualists 
themselves,  might  underlie  their  manifestations.  Extraor- 
dinary effects  are  produced  by  the  accumulation  of  small 
impulses.  Galileo  set  a  heavy  pendulum  in  motion  by  the 
well-timed  puffs  of  his  breath.  Ellicot  set  one  clock  going 
by  the  ticks  of  another,  even  when  the  two  clocks  were 
separated  by  a  wall.  Preconceived  notions  can,  moreover, 
vitiate,  to  an  extraordinary  degree,  the  testimony  of  even 
veracious  persons.  Hence  my  desire  to  witness  those  ex- 
traordinary phenomena,  the  existence  of  which  seemed 
placed  beyond  a  doubt  by  the  known  veracity  of  those  who 
had  witnessed  and  described  them.  The  meeting  took 


SCIENCE  AND   SPIRITS.  403 

place  at  a  private  residence  in  the  neighborhood  of  Lon- 
don. My  host,  his  intelligent  wife,  and  a  gentleman  who 
may  be  called  X.,  were  in  the  house  when  I  arrived.  I 
was  informed  that  the  "  medium "  had  not  yet  made  her 
appearance  ;  that  she  was  sensitive,  and  might  resent  sus- 
picion. It  was  therefore  requested  that  the  tables  and 
chairs  should  be  examined  before  her  arrival,  in  order  to  be 
assured  that  there  was  no  trickery  in  the  furniture.  This 
was  done ;  and  I  then  first  learned  that  my  hospitable  host 
had  arranged  that  the  seance  should  be  a  dinner-party. 
This  was  to  me  an  unusual  form  of  investigation ;  but  I 
accepted  it,  as  one  of  the  accidents  of  the  occasion. 

The  "  medium  "  arrived — a  delicate-looking  young  lady, 
who  appeared  to  have  suffered  much  from  ill  health.  I 
took  her  to  dinner  and  sat  close  beside  her.  Facts  were 
absent  for  a  considerable  time,  a  series  of  very  wonderful 
narratives  supplying  their  place.  The  duty  of  belief  on 
testimony  was  frequently  insisted  on.  X.  appeared  to  be 
a  chosen  spiritual  agent,  and  told  us  many  surprising 
things.  He  affirmed  that,  when  he  took  a  pen  in  his  hand, 
an  influence  ran  from  his  shoulder  downward,  and  impelled 
him  to  write  oracular  sentences.  I  listened  for  a  time, 
offering  no  observation.  "  And  now,"  continued  X.,  "  this 
power  has  so  risen  as  to  reveal  to  me  the  thoughts  of  others. 
Only  this  morning  I  told  a  friend  what  he  was  thinking  of, 
and  what  he  intended  to  do  during  the  day."  Here,  I 
thought,  is  something  that  can  be  at  once  tested.  I  said 
immediately  to  X. :  "  If  you  wish  'to  win  to  your  cause  an 
apostle,  who  will  proclaim  your  principles  to  the  world 
without  fear,  tell  me  what  I  am  now  thinking  of."  X. 
reddened,  and  did  not  tell  me  my  thought. 

Some  time  previously  I  had  visited  Baron  Reichenbach, 
in  Vienna,  and  I  now  asked  the  young  lady  who  sat  beside 
me,  whether  she  could  see  any  of  the  curious  things  which 
he  describes — the  light  emitted  by  crystals,  for  example  ? 


404  FRAGMENTS  OF  SCIENCE, 

Here  is  the  conversation  which  followed,  as  extracted  from 
my  notes,  written  on  the  day  following  the  seance  : 

Medium. — "  Oh,  yes ;  but  I  see  light  around  all 
bodies." 

Z — "  Even  in  perfect  darkness  ?  " 

Medium. — "  Yes ;  I  see  luminous  atmospheres  round  all 
people.  The  atmosphere  which  surrounds  Mr.  R.  C.  would 
fill  this  room  with  light." 

I. — "  You  are  aware  of  the  effects  ascribed  by  Baron 
Reichenbach  to  magnets  ?  " 

Medium. — "  Yes ;  but  a  magnet  makes  me  terribly  ill." 

Z — "  Am  I  to  understand  that,  if  this  room  were  per- 
fectly dark,  you  could  tell  whether  it  contained  a  magnet, 
without  being  informed  of  the  fact  ?  " 

Medium. — "  I  should  know  of  its  presence  on  entering 
the  room." 

Z— "How?" 

Medium.—'-''  I  should  be  rendered  instantly  ill." 

Z— "  How  do  you  feel  to-day  ?  " 

Medium. — "  Particularly  well ;  I  have  not  been  so  well 
for  months." 

Z — "  Then,  may  I  ask  you  whether  there  is,  at  the 
present  moment,  a  magnet  in  my  possession  ?  " 

The  young  lady  looked  at  me,  blushed,  and  stammered, 
"  No ;  I  am  not  en  rapport  with  you." 

I  sat  at  her  right  hand,  and  a  left-hand  pocket,  within 
six  inches  of  her  person,  contained  a  magnet. 

Our  host  here  deprecated  discussion,  as  it  "  exhausted 
the  medium."  The  wonderful  narratives  were  resumed ; 
but  I  had  narratives  of  my  own  quite  as  wonderful.  These 
spirits  indeed,  seemed  clumsy  creations,  compared  with 
those  with  which  my  own  researches  had  made  me  familiar. 
I  therefore  began  to  match  the  wonders  related  to  me  by 
other  wonders.  A  lady  present  discoursed  on  spiritual 
atmospheres,  which  she  could  see  as  beautiful  colors  when 


SCIENCE  AND   SPIRITS.  405 

she  closed  her  eyes.  I  professed  myself  able  to  see  similar 
colors,  and  more  than  that,  to  be  able  to  see  the  interior  of 
my  own  eyes.  The  medium  affirmed  that  she  could  see 
actual  waves  of  light  coming  from  the  sun.  I  retorted  that 
men  of  science  could  tell  the  exact  number  of  waves 
emitted  in  a  second,  and  also  their  exact  length.  The 
medium  spoke  of  the  performances  of  the  spirits  on  musical 
instruments.  I  said  that  such  performance  was  gross,  in 
comparison  with  a  kind  of  music  which  had  been  discovered 
some  time  previously  by  a  scientific  man.  Standing  at  a 
distance  of  twenty  feet  from  a  jet  of  gas,  he  could  command 
the  flame  to  emit  a  melodious  note ;  it  would  obey,  and 
continue  its  song  for  hours.  So  loud  was  the  music  emitted 
by  the  gas-flame,  that  it  might  be 'heard  by  an  assembly  of 
a  thousand  people.  These  were  acknowledged  to  be  as 
great  marvels  as  any  of  those  of  spiritdom.  The  spirits 
were  then  consulted,  and  I  was  pronounced  to  be  a  first- 
class  medium. 

During  this  conversation  a  low  knocking  was  heard 
from  time  to  time  under  the  table.  These  were  the  spirits' 
knocks.  I  was  informed  that  one  knock,  in  answer  to  a 
question,  meant  "  No ; "  that  two  knocks  meant  "  Not 
yet ;  "  and  that  three  knocks  meant  "  Yes."  In  answer  to 
the  question  whether  I  was  a  medium,  the  response  was 
three  brisk  and  vigorous  knocks.  I  noticed  that  the  knocks 
issued  from  a  particular  locality,  and  therefore  requested 
the  spirits  to  be  good  enough  to  answer  from  another 
corner  of  the  table.  They  did  not  comply;  but  I  was 
assured  that  they  would  do  it,  and  much  more,  by-and-by. 
The  knocks  continuing,  I  turned  a  wine-glass  upside  down, 
and  placed  my  ear  upon  it,  as  upon  a  stethoscope.  The 
spirits  seemed  disconcerted  by  the  act ;  they  lost  their 
playfulness,  and  did  not  quite  recover  it  for  a  considerable 
time. 

Somewhat  weary  of  the  proceedings,  I  once  threw  my- 


406  FRAGMENTS  OF  SCIENCE. 

self  back  against  my  chair,  and  gazed  listlessly  out  of  the 
window.  While  thus  engaged,  the  table  was  rudely  pushed. 
Attention  was  drawn  to  the  wine,  still  oscillating  in  the 
glasses,  and  I  was  asked  whether  that  was  not  convincing. 
I  readily  granted  the  fact  of  motion,  and  began  to  feel  the 
delicacy  of  my  position.  There  were  several  pairs  of  arms 
upon  the  table,  and  several  pairs  of  legs  under  it ;  but  how 
was  I,  without  offence,  to  express  the  conviction  which  I 
really  entertained?  To  ward  off  the  difficulty,  I  again 
turned  a  wine-glass  upside  down  and  rested  my  ear  upon  it. 
The  rim  of  the  glass  was  not  level,  and  the  hair  on  touch- 
ing it  caused  it  to  vibrate  and  produce  a  peculiar  buzzing 
sound.  A  perfectly  candid  and  warm-hearted  old  gentle- 
man at  the  opposite  side  of  the  table,  whom  I  may  call  A., 
drew  attention  to  the  sound,  and  expressed  his  entire  belief 
that  it  was  spiritual.  I,  however,  informed  him  that  it  was 
the  moving  hair  acting  on  the  glass.  The  explanation  was 
not  well  received,  and  X.,  in  a  tone  of  severe  pleasantry, 
demanded  whether  it  was  the  hair  that  had  moved  the 
table.  The  promptness  of  my  negative  probably  satisfied 
him  that  my  notion  was  a  very  different  one. 

The  superhuman  power  of  the  spirits  was  next  dwelt 
upon.  The  strength  of  man,  it  was  stated,  was  unavailing 
in  opposition  to  theirs.  No  human  power  could  prevent 
the  table  from  moving  when  they  pulled  it.  During  the 
evening  this  pulling  of  the  table  occurred,  or  rather  was 
attempted,  three  times.  Twice  the  table  moved  when  my 
attention  was  withdrawn  from  it ;  on  a  third  occasion,  I 
tried  whether  the  act  could  be  provoked  by  an  assumed  air 
of  inattention.  Grasping  the  table  firmly  between  my 
knees,  I  threw  myself  back  in  the  chair,  and  waited,  with 
eyes  fixed  on  vacancy,  for  the  pull.  It  came.  For  some 
seconds  it  was  pull  spirit,  hold  muscle  ;  the  muscle,  how- 
ever, prevailed,  and  the  table  remained  at  rest.  Up  to  the 
present  moment,  this  interesting  fact  is  known  only  to  the 
particular  spirit  in  question  and  myself. 


SCIENCE  AND   SPIRITS.  407 

A  species  of  mental  scene-painting,  with  which  my  own 
pursuits  had  long  rendered  me  familiar,  was  employed  to 
figure  the  changes  and  distribution  of  spiritual  power. 
The  spirits  were  provided  with  atmospheres,  which  com- 
bined with  and  interpenetrated  each  other,  considerable 
ingenuity  being  shown  in  demonstrating  the  necessity  of 
time  in  effecting  the  adjustment  of  the  atmospheres.  In 
fact,  just  as  in  science,  the  senses,  time,  and  space,  con- 
stituted the  conditions  of  the  phenomena.  A  rearrange- 
ment of  our  positions  was  proposed  and  carried  out ;  and 
soon  afterward  my  attention  was  drawn  to  a  scarcely 
sensible  vibration  on  the  part  of  the  table.  Several  persons 
were  leaning  on  the  table  at  the  time,  and  I  asked  permis- 
sion to  touch  the  medium's  hand.  "  Oh,  I  know  I  tremble," 
was  her  reply.  Throwing  one  leg  across  the  other,  I  ac- 
cidentally nipped  a  muscle,  and  produced  thereby  an  in- 
voluntary vibration  of  the  free  leg.  This  vibration,  I  knew, 
must  be  communicated  to  the  floor,  and  thence  to  the 
chairs  of  all  present.  I  therefore  intentionally  promoted  it. 
My  attention  was  promptly  drawn  to  the  motion ;  and  a 
gentleman  beside  me,  whose  value  as  a  witness  I  was  par- 
ticularly desirous  to  test,  expressed  his  belief,  that  it  was 
out  of  the- compass  of  human  power  to  produce  so  strange 
a  tremor.  "  I  believe,"  he  added  earnestly,  "  that  it  is 
entirely  the  spirits'  work."  "  So  do  I,"  added,  with  heat, 
the  candid  and  warm-hearted  old  gentleman  A.  "  Why, 
sir,"  he  continued,  "  I  feel  them  at  this  moment  shaking 
my  chair."  I  stopped  the  motion  of  the  leg.  "  Now,  sir," 
A.  exclaimed,  "  They  are  gone."  I  began  again,  and  A. 
once  more  ejaculated.  I  could,  however,  notice  that  there 
were  doubters  present,  who  did  not  quite  know  what  to 
think  of  the  manifestations.  I  saw  their  perplexity ;  and, 
as  there  was  sufficient  reason  to  believe  that  the  disclosure 
of  the  secret  would  simply  provoke  anger,  I  kept  it  to 
myself. 


408  FRAGMENTS  OF  SCIENCE. 

Again  a  period  of  conversation  intervened,  during  which 
the  spirits  became  animated.  The  evening  was  confessedly 
a  dull  one,  but  matters  appeared  to  brighten  toward  its 
close.  The  spirits  were  requested  to  spell  the  name  by 
which  I  am  known  in  the  heavenly  world.  Our  host  com- 
menced repeating  the  alphabet,  and  when  he  reached  the 
letter  "  P  "  a  knock  was  heard.  He  began  again,  and  the 
spirits  knocked  at  the  letter  "  O."  I  was  puzzled,  but 
waited  for  the  end.  The  next  letter  knocked  down  was 
"  E."  I  laughed,  and  remarked  that  the  spirits  were  going 
to  make  a  poet  of  me.  Admonished  for  my  levity,  I  was 
informed  that  the  frame  of  mind  proper  for  the  occasion 
ought  to  have  been  superinduced  by  a  perusal  of  the  Bible 
immediately  before  the  stance.  The  spelling,  however, 
went  on,  and  sure  enough  I  came  out  a  poet.  But  matters 
did  not  end  here.  Our  host  continued  his  repetition  of  the 
alphabet,  and  the  next  letter  of  the  name  proved  to  be 
"  O."  Here  was  manifestly  an  unfinished  word ;  and  the 
spirits  were  apparently  in  their  most  communicative  mood. 
The  knocks  came  from  under  the  table,  but  no  person  pres- 
ent evinced  the  slightest  desire  to  look  under  it.  I  asked 
whether  I  might  go  underneath ;  the  permission  was 
granted ;  so  I  crept  under  the  table.  Some  tittered ;  but 
the  candid  old  A.  exclaimed,  "  He  has  a  right  to  look  into 
the  very  dregs  of  it,  to  convince  himself."  Having  pretty 
well  assured  myself  that  no  sound  could  be  produced  under 
the  table  without  its  origin  being  revealed,  I  requested  our 
host  to  continue  his  questions.  He  did  so,  but  in  vain.  He 
adopted  a  tone  of  tender  entreaty ;  but  the  "  dear  spirits  " 
had  become  dumb  dogs,  and  refused  to  be  entreated.  I 
continued  under  that  table  for  at  least  a  quarter  of  an  hour, 
after  which,  with  a  feeling  of  despair  as  regards  the  pros- 
pects of  humanity  never  before  experienced,  I  regained  my 
chair.  Once  there,  the  spirits  resumed  their  loquacity,  and 
dubbed  me  "  Poet  of  Science." 


SCIENCE  AND  SPIRITS.  409 

This,  then,  is  the  result  of  an  attempt  made  by  a  scien- 
tific man  to  look  into  these  spiritual  phenomena.  It  is  not 
encouraging ;  and  for  this  reason :  The  present  promoters 
of  spiritual  phenomena  divide  themselves  into  two  classes, 
one  of  which  needs  no  demonstration,  while  the  other  is 
beyond  the  reach  of  proof.  The  victims  like  to  believe,  and 
they  do  not  like  to  be  undeceived.  Science  is  perfectly 
powerless  in  the  presence  of  this  frame  of  mind.  It  is, 
moreover,  a  state  perfectly  compatible  with  extreme  intel- 
lectual subtlety  and  a  capacity  for  devising  hypotheses 
which  only  require  the  hardihood  engendered  by  strong 
conviction,  or  by  callous  mendacity,  to  render  them  impreg- 
nable. The  logical  feebleness  of  science  is  not  sufficiently 
borne  in  mind.  It  keeps  down  the  weed  of  superstition, 
not  by  logic  but  by  slowly  rendering  the  mental  soil  unfit 
for  its  cultivation.  When  science  appeals  to  uniform  ex- 
perience, the  spiritualist  will  retort,  "  How  do  you  know 
that  a  uniform  experience  will  continue  uniform  ?  You  tell 
me  that  the  sun  has  risen  for  six  thousand  years  :  that  is 
no  proof  that  it  will  rise  to-morrow ;  within  the  next  twelve 
hours  it  may  be  puffed  out  by  the  Almighty."  Taking  this 
ground,  a  man  may  maintain  the  story  of  "  Jack  and  the 
Bean-stalk "  in  the  face  of  all  the  science  in  the  world. 
You  urge,  in  vain,  that  science  has  given  us  all  the  knowl- 
edge of  the  universe  which  we  now  possess,  while  spiritual- 
ism has  added  nothing  to  that  knowledge.  The  drugged 
soul  is  beyond  the  reach  of  reason.  It  is  in  vain  that  im- 
postors are  exposed,  and  the  special  demon  cast  out.  He 
has  but  slightly  to  change  his  shape,  return  to  his  house, 
and  find  it  "  empty,  swept,  and  garnished."  * 

December  10,  1864. 


18 


VITALITY. 

THE  origin,  growth,  and  energies  of  living  things  are 
subjects  which  have  always  engaged  the  attention  of  think- 
ing men.  To  account  for  them  it  was  usual  to  assume  a 
special  agent,  to  a  great  extent  free  from  the  limitations 
observed  among  the  powers  of  inorganic  Nature.  This 
agent  was  called  the  vital  force  ;  and,  under  its  influence, 
plants  and  animals  were  supposed  to  collect  their  materials 
and  to  assume  determinate  forms.  Within  the  last  twenty 
years,  however,  our  ideas  of  vital  processes  have  undergone 
profound  modifications ;  and  the  interest,  and  even  dis- 
quietude, which  the  change  has  excited  in  some  minds  are 
amply  evidenced  by  the  discussions  and  protests  which  are 
now  common  regarding  the  phenomena  of  vitality.  In 
tracing  out  these  phenomena  through  all  their  modifications 
the  most  advanced  philosophers  of  the  present  day  declare 
that  they  ultimately  arrive  at  a  single  source  of  power, 
from  which  all  vital  energy  is  derived ;  and  the  disquieting 
circumstance  is  that  this  source  is  not  the  direct  fiat  of  a 
supernatural  agent,  but  a  reservoir  of  what,  if  we  do  not 
accept  the  creed  of  Zoroaster,  must  be  regarded  as  inor- 
ganic force.  In  short,  it  is  considered  as  proved  that  all 
the  energy  which  we  derive  from  plants  and  animals  is 
drawn  from  the  sun. 

A  few  years  ago,  when  the  sun  was  affirmed  to  be  the 
source  of  life,  nine  out  of  ten  of  those  who  are  alarmed  by 
the  form  which  this  assertion  has  latterly  assumed,  would 
have  assented,  in  a  general  way,  to  its  correctness,.  Their 
assent,  however,  was  more  poetical  than  scientific,  and  they 


VITALITY.  411 

were  by  no  means  prepared  to  see  a  rigid  mechanical  sig- 
nification attached  to  their  words.  This,  however,  is  the 
peculiarity  of  modern  conclusions :  that  there  is  no  creative  f 
energy  whatever  in  the  vegetable  or  animal  organism,  but 
that  all  the  power  which  we  obtain  from  the  muscles  of 
men  and  animals,  as  much  as  that  which  we  develop  by 
the  combustion  of  wood  or  coal,  has  been  produced  at  the 
sun's  expense.  The  sun  is  so  much  colder  that  we  may 
have  our  fires ;  he  is  also  so  much  colder  that  we  may  have 
our  horse-racing  and  Alpine  climbing.  It  is,  for  example, 
certain  that  the  sun  has  been  chilled  to  an  extent  capable 
of  being  accurately  expressed  in  numbers,  in  order  to  fur- 
nish the  power  which  lifted  this  year  a  certain  number  of 
tourists  from  the  vale  of  Chamouni  to  the  summit  of  Mont 
Blanc. 

To  most  minds,  however,  the  energy  of  light  and  heat 
presents  itself  as  a  thing  totally  distinct  from  ordinary  me- 
chanical energy.  But  either  of  them  can  be  derived  from 
the  other.  By  the  friction  of  wood  a  savage  can  raise  it 
to  the  temperature  of  ignition ;  by  properly  striking  a  piece 
of  iron  a  skilful  blacksmith  can  cause  it  to  glow,  and  thus, 
by  the  rude  agency  of  his  hammer,  he  generates  light  and 
heat.  This  action,  if  carried  far  enough,  would  produce  the 
light  and  heat  of  the  sun.  In  fact  the  sun's  light  and  heat 
have  actually  been  referred  to  the  fall  of  meteoric  matter 
upon  his  surface  ;  and  whether  the  sun  is  thus  supported  or 
not,  it  is  perfectly  certain  that  he  might  be  thus  supported. 
Whether,  moreover,  the  whilom  molten  condition  of  our 
planet  was,  as  supposed  by  eminent  men,  due  to  the  collision 
of  cosmic  masses  or  not,  it  is  perfectly  certain  that  the  mol- 
ten condition  might  be  thus  brought  about,  pf,  then,  solar 
light  and  heat  can  be  produced  by  the  impact  of  dead  mat- 
ter, and  if  from  the  light  and  heat  thus  produced  we  can 
derive  the  energies  which  we  have  been  accustomed  to  call 
vital.,  it  indubitably  follows  that  vital  energy  may  have  a  \ 
proximately  mechanical  origin. 


412  FRAGMENTS  OF  SCIENCE. 

In  what  sense,  then,  is  the  sun  to  be  regarded  as  the 
origin  of  the  energy  derivable  from  plants  and  animals  ? 
Let  us  try  to  give  an  intelligible  answer  to  this  question. 
Water  may  be  raised  from  the  sea-level  to  a  high  elevation, 
and  then  permitted  to  descend.  In  descending  it  may  be 
made  to  assume  various  forms — to  fall  in  cascades,  to  spurt 
in  fountains,  to  boil  in  eddies,  or  to  flow  tranquilly  along  a 
uniform  bed.  It  may,  moreover,  be  caused  to  set  complex 
machinery  in  motion,  to  turn  mill-stones,  throw  shuttles, 
work  saws  and  hammers,  and  drive  piles.  But  every  form 
of  power  here  indicated  would  be  derived  from  the  original 
power  expended  in  raising  the  water  to  the  height  from 
which  it  fell.  There  is  no  energy  generated  by  the  ma- 
chinery ;  the  work  performed  by  the  water  in  descending 
is  merely  the  parcelling  out  and  distribution  of  the  work 
expended  in  raising  it.  In  precisely  this  sense  is  all  the 
energy  of  plants  and  animals  the  parcelling  out  and  distri- 
bution of  a  power  originally  exerted  by  the  sun.  In  the 
case  of  the  water,  the  source  of  the  power  consists  in  the 
forcible  separation  of  a  quantity  of  the  liquid  from  a  low 
level  of  the  earth's  surface  and  its  elevation  to  a  higher 
position,  the  power  thus  expended  being  returned  by  the 
water  in  its  descent.  In  the  case  of  vital  phenomena,  the 
source  of  power  consists  in  the  forcible  separation  of  the 
atoms  of  compound  substances  by  the  sun.  We  name  the 
force  which  draws  the  water  earthward  "  gravity,"  and  that 
which  draws  atoms  together  "  chemical  affinity ; "  but  these 
different  names  must  not  mislead  us  regarding  the  qualita- 
tive identity  of  the  two  forces.  They  are  both  attractions, 
and,  to  the  intellect,  the  falling  of  carbon  atoms  against 
oxygen  atoms  is  not  more  difficult  of  conception  than  the 
falling  of  water  to  the  earth. 

The  building  up  of  the  vegetable,  then^  is  effected  by 
the  sun  through  the  reduction  of  chemical  compounds.  The 
phenomena  of  animal  life  are  more  or  less  complicated 


VITALITY.  413 

reversals  of  these  processes  of  reduction.  We  eat  the  vege- 
table, and  we  breathe  the  oxygen  of  the  air,  and  in  our 
bodies  the  oxygen  which  had  been  lifted  from  the  carbon 
and  hydrogen  by  the  action  of  the  sun  again  falls  toward 
them,  producing  animal  heat  and  developing  animal  forms. 
Through  the  most  complicated  phenomena  of  vitality  this 
law  runs  :  the  vegetable  is  produced  while  a  weight  rises, 
the  animal  is  produced  while  a  weight  falls.  But  the  ques- 
tion is  not  exhausted  here.  The  water  employed  in  our 
first  illustration  generates  all  the  motion  displayed  in  its 
descent,  but  the  form  of  the  motion  depends  on  the  charac- 
ter of  the  machinery  interposed  in  the  path  of  the  water. 
In  a  similar  way  the  primary  action  of  the  sun's  rays  is 
qualified  by  the  atoms  and  molecules  among  which  their 
energy  is  distributed.  Molecular  forces  determine  the  form 
which  the  solar  energy  will  assume.  In  the  separation  of 
the  carbon  and  oxygen  this  energy  may  be  so  conditioned 
as  to  result  in  one  case  in  the  formation  of  a  cabbage,  and 
in  another  case  in  the  formation  of  an  oak.  So  also  as 
regards  the  reunion  of  the  carbon  and  the  oxygen,  the  mo- 
lecular machinery  through  which  the  combining  energy 
acts  may,  in  one  case,  weave  the  texture  of  a  frog,  while 
in  another  it  may  weave  the  texture  of  a  man. 

The  matter  of  the  animal  body  is  that  of  inorganic  Na- 
ture. There  is  no  substance  in  the  animal  tissues  which  is 
not  primarily  derived  from  the  rocks,  the  water,  and  the 
air.  Are  the  forces  of  organic  matter,  then,  different  in 
kind  from  those  of  inorganic  matter  ?  The  philosophy  of 
the  present  day  negatives  the  question.  It  is  the  com- 
pounding in  the  organic  world  of  forces  belonging  equally 
to  the  inorganic  that  constitutes  the  mystery  and  the  mir- 
acle of  vitality.  Every  portion  of  every  animal  body  may 
be  reduced  to  purely  inorganic  matter.  A  perfect  reversal 
of  this  process  of  reduction  would  carry  us  from  the  inor- 
ganic to  the  organic ;  and  such  a  reversal  is  at  least  con- 


414  .  FRAGMENTS  OF  SCIENCE. 

ceivable.  The  tendency,  indeed,  of  modern  science  is  to 
break  down  the  wall  of  partition  between  organic  and  inor- 
ganic, and  to  reduce  both  to  the  operation  of  forces  which 
are  the  same  in  kind,  but  whose  combinations  differ  in  com- 
plexity. 

Consider  now  the  question  of  personal  identity,  in  rela- 
tion to  this  of  molecular  form.  Twenty-six  years  ago, 
Mayer,  of  Heilbronn,  with  that  power  of  genius  which 
breathes  large  meanings  into  scanty  facts,  pointed  out  that 
the  blood  was  "  the  oil  of  life,"  the  combustion  of  which, 
like  that  of  coal  in  grosser  cases,  sustained  muscular  action. 
The  muscles  are  the  machinery  by  which  the  dynamic  power 
of  the  blood  is  brought  into  play.  Thus  the  blood  is  con- 
sumed. But  the  whole  body,  though  more  slowly  than  the 
blood,  wastes  also,  so  that  after  a  certain  number  of  years 
it  is  entirely  renewed.  How  is  the  sense  of  personal  iden- 
tity maintained  across  this  flight  of  molecules  ?  To  man  as 
we  know  him,  matter  is  necessary  to  consciousness,  but  the 
matter  of  any  period  may  be  all  changed,  while  conscious- 
ness exhibits  no  solution  of  continuity.  Like  changing 
sentinels,  the  oxygen,  hydrogen,  and  carbon  that  depart 
seem  to  whisper  their  secret  to  their  comrades  that  arrive, 
and  thus,  while  the  Non-ego  shifts  the  Ego  remains  intact. 
Constancy  of  form  in  the  grouping  of  the  molecules,  and 
not  constancy  of  the  molecules  themselves,  is  the  correlative 
of  this  constancy  of  perception.  Life  is  a  wave  which  in 
no  two  consecutive  moments  of  its  existence  is  composed 
of  the  same  particles. 

Supposing,  then,  the  melocules  of  the  human  body 
instead  of  replacing  others,  and  thus  renewing  a  preexist- 
ing form,  to  be  gathered  first  hand  from  Nature  and  put 
together  in  the  same  relative  positions  as  those  which  they 
occupy  in  the  body ;  that  they  have  the  self-same  forces  and 
distribution  of  forces,  the  self-same  motions  and  distribution 
of  motions — would  this  organized  concourse  of  molecules 


VITALITY,  415 

stand  before  us  as  a  sentient  thinking  being  ?  There  seerns 
no  valid  reason  to  believe  that  it  would  not.  Or,  supposing 
a  planet  carved  from  the  sun,  and  set  spinning  round  ail 
axis,  and  revolving  round  the  sun  at  a  distance  from  him 
equal  to  that  of  our  earth,  would  one  of  the  consequences 
of  its  refrigeration  be  the  development  of  organic  forms  ? 
I  lean  to  the  affirmative.  Structural  forces  are  certainly 
in  the  mass,  whether  or  not  those  forces  reach  to  the  extent 
of  forming  a  plant  or  an  animal.  In  an  amorphous  drop  of 
water  lie  latent  all  the  marvels  of  crystalline  force ;  and 
who  will  set  limits  to  the  possible  play  of  molecules  in  a 
cooling  planet  ?  If  these  statements  startle,  it  is  because 
matter  has  been  denned  and  maligned  by  philosophers  and 
theologians  who  were  equally  unaware  that  it  is,  at  bottom, 
essentially  mystical  and  transcendental. 

Questions  such  as  these  derive  their  present  interest  in 
great  part  from  their  audacity,  which  is  sure,  in  due  time,  to 
disappear.  And  the  sooner  the  public  dread  is  abolished 
with  reference  to  such  questions  the  better  for  the  cause  of 
truth.  As  regards  knowledge,  physical  science  is  polar. 
In  one  sense  it  knows,  or  is  destined  to  know,  every  thing. 
In  another  sense  it  knows  nothing.  Science  knows  much 
of  this  intermediate  phase  of  things  that  we  call  Nature,  of 
which  it  is  the  product ;  but  science  knows  nothing  of  the 
origin  or  destiny  of  Nature.  Who  or  what  made  the  sun, 
and  gave  his  rays  their  alleged  power  ?  Who  or  what  made 
and  bestowed  upon  the  ultimate  particles  of  matter  their 
wondrous  power  of  varied  interaction  ?  Science  does  not 
know :  the  mystery,  though  pushed  back,  remains  unaltered. 
To  many  of  us  who  feel  that  there  are  more  things  in 
heaven  and  earth  than  are  dreamt  of  in  the  present  phi' 
losophy  of  science,  but  who  have  been  also  taught,  by 
baffled  efibrts,  how  vain  is  the  attempt  to  grapple  with 
the  inscrutable,  the  ultimate  frame  of  mind  is  that  of 
Goethe: 


416  FRAGMENTS  OF  SCIENCE. 

"Who  dares  to  name  His  name, 
Or  belief  in  Him  proclaim, 
Veiled  in  mystery  as  He  is,  the  All-enfolder  ? 
Gleams  across  the  mind  His  light, 
Feels  the  lifted  soul  His  might, 
Dare  it  then  deny  His  reign,  the  All-upholder?  " 


One  or  two  interpolations  excepted,  the  foregoing  brief 
article  was  written  on  an  Alpine  slope  in  the  summer  of 
1863.  Seven  years  afterward  I  was  singularly  interested 
to  learn,  that  nearly  300  years  ago,  in  explaining  the  actions 
and  energies  of  the  human  body,  Descartes  employed 
similar  imagery  and  expressed  similar  views  as  far  as  the 
knowledge  of  his  time  allowed.  Professor  Huxley,  who 
possesses  a  reading  faculty  which  I  can  but  envy,  has  pub- 
lished in  his  "  Lay  Sermons  "  the  following  remarkable 
extracts  from  the  "  Traite  de  1'Homme  :  " 

"  In  proportion  as  these  spirits  "  (the  animal  spirits)  "  enter  the  cavi- 
ties of  the  brain,  they  pass  thence  into  the  pores  of  its  substance,  and  from 
these  pores  into  the  nerves ;  where,  according  as  they  enter,  or  even 
only  tend  to  enter,  more  or  less,  into  one  than  into  another,  they  have 
the  power  of  altering  the  figure  of  the  muscles  into  which  the  nerves  are 
inserted,  and  by  this  means  of  causing  all  the  limbs  to  move.  Thus,  aa 
you  may  have  seen  in  the  grottoes  and  the  fountains  in  royal  gardens, 
the  force  with  which  the  water  issues  from  its  reservoir  is  sufficient  to 
move  various  machines,  and  even  to  make  them  play  instruments,  or 
pronounce  words,  according  to  the  different  disposition  of  the  pipes  which 
lead  the  water. 

"  And,  in  truth,  the  nerves  of  the  machine  which  I  am  describing  may 
very  well  be  compared  to  the  pipes  of  these  water-works ;  its  muscles 
and  its  tendons  to  the  other  various  engines  and  springs  which  seem  to 
move  them ;  its  animal  spirits  to  the  water  which  impels  them,  of  which 
the  heart  is  the  fountain ;  while  the  cavities  of  the  brain  are  the  central 
office.  Moreover,  respiration  and  other  such  actions  as  are  natural  and 
usual  in  the  body,  and  which  depend  on  the  course  of  the  spirits,  are 
like  the  movements  of  a  clock,  or  of  a  mill,  which  may  be  kept  up  by  the 
ordinary  flow  of  water. 


VITALITY.  417 

"  The  external  objects  which,  by  their  mere  presence,  act  upon  the 
organs  of  the  senses  ;  and  which,  by  this  means,  determine  the  corporal 
machine  to  move  in  many  different  ways,  according  as  the  parts  of  the 
brain  are  arranged,  are  like  the  strangers  who,  entering  into  some  of  the 
grottoes  of  those  water- works,  unconsciously  cause  the  movements  which 
take  place  in  their  presence.  For  they  cannot  enter  without  treading  upon 
certain  planks  so  arranged  that,  for  example,  if  they  approach  a  bathing 
Diana,  they  cause  her  to  hide  among  the  reeds ;  and  if  they  attempt  to 
follow  her,  they  see  approaching  a  Neptune,  who  threatens  them  with  his 
trident ;  or  if  they  try  some  other  way,  they  cause  some  monster  who 
vomits  water  into  their  faces,  to  dart  out ;  or  like  contrivances,  according 
to  the  fancy  of  the  engineers  who  have  made  them.  And  lastly,  when 
the  rational  soul  is  lodged  in  this  machine,  it  will  have  its  principal  seat 
in  the  brain,  and  will  take  the  place  of  the  engineer,  who  ought  to  be 
in  that  part  of  the  works  with  which  all  the  pipes  are  connected,  when 
he  wishes  to  increase,  or  to  slacken,  or  in  some  way  to  alter,  their  move- 
ments." 

"  All  the  functions  which  I  have  attributed  to  this  machine "  (the 
body),  "  as  the  digestion  of  food,  the  pulsation  of  the  heart  and  of  the 
arteries  ;  the  nutrition  and  the  growth  of  the  limbs ;  respiration,  wake- 
fulness,  and  sleep ;  the  reception  of  light,  sounds,  odors,  flavors,  heat,  and 
such  like  qualities,  in  the  organs  of  the  external  senses ;  the  impression 
of  the  ideas  of  these  in  the  organ  of  common-sense  and  in  the  imagina- 
tion ;  the  retention,  or  the  impression,  of  these  ideas  on  the  memory ; 
the  internal  movements  of  the  appetites  and  the  passions ;  and  lastly, 
the  external  movements  of  all  the  limbs,  which  follow  so  aptly,  as  well 
the  action  of  the  objects  which  are  presented  to  the  senses,  as  the  im- 
pressions which  meet  in  the  memory,  that  they  imitate  as  nearly  as 
possible  those  of  a  real  man :  I  desire,  I  say,  that  you  should  consider 
that  these  functions  hi  the  machine  naturally  proceed  from  the  mere 
arrangement  of  its  organs,  neither  more  nor  less  than  do  the  movements 
of  a  clock,  or  other  automaton,  from  that  of  its  weights  and  its  wheels ; 
so  that,  so  far  as  these  are  concerned,  it  is  not  necessary  to  conceive  any 
other  vegetative  or  sensitive  soul,  nor  any  other  principle  of  motion,  or 
of  life,  than  the  blood  and  the  spirits  agitated  by  the  fire  which  burns 
continually  in  the  heart,  and  which  is  no  wise  essentially  different  from 
all  the  fires  which  exist  in  inanimate  bodies." 


ADDITIONAL  REMARKS  ON  MIRACLES. 


AMONG  the  scraps  of  manuscript  written  at  the  time 
when  Mr.  Mozley's  work  occupied  my  attention  I  find  the 
following  reflections : 

With  regard  to  the  influence  of  modern  science  which 
Mr.  Mozley  rates  so  low,  one  effect  of  it  is  certainly  to  en- 
hance the  magnitude  of  many  of  the  recorded  miracles,  and 
to  increase  proportionably  the  difficulties  of  belief.  The 
ancients  knew  but  little  of  the  vastness  of  the  universe. 
The  Rev.  Mr.  Kirkman,  for  example,  has  shown  what  inad- 
equate notions  the  Jews  entertained  regarding  the  "  firma- 
ment of  heaven ; "  and  Professor  Airy  refers  to  the  case  of 
a  Greek  philosopher  who  was  persecuted  for  hazarding  the 
assertion,  then  deemed  monstrous,  that  the  sun  might  be  as 
large  as  the  whole  country  of  Greece.  The  concerns  of  a 
universe,  regarded  from  this  point  of  view,  were  vastly 
more  commensurate  with  man  and  his  concerns  than  those 
of  the  universe  which  science  now  reveals  to  us ;  and  hence 
that  to  suit  man's  purposes,  or  in  compliance  with  his 
prayers,  changes  should  occur  in  the  order  of  the  universe, 
was  more  easy  of  belief  in  the  ancient  world  than  it  can 
be  now.  In  the  very  magnitude  which  it  assigns  to  natural 
phenomena,  science  has  augmented  the  distance  between 
them  and  man,  and  increased  the  popular  belief  in  their  or- 
derly progression.  As  a  natural  consequence,  the  demand 


REMAKES  ON  MIRACLES.  419 

for  evidence  is  more  exacting  than  it  used  to  be,  whenever 
it  is  affirmed  that  such  order  has  been  disturbed. 

Let  us  take  as  an  illustration  the  miracle  by  which  the 
victory  of  Joshua  over  the  Amorites  was  rendered  complete, 
where  the  sun  is  reported  to  have  stood  still  for  "  a  whole 
day"  upon  Gibeon,  and  the  moon  in  the  valley  of  Ajalon. 
An  Englishman  of  average  education  at  the  present  day 
would  naturally  demand  a  greater  amount  of  evidence  to 
prove  that  this  occurrence  took  place  than  would  have  sat- 
isfied an  Israelite  in  the  age  succeeding  that  of  Joshua. 
For,  to  the  one,  the  miracle  probably  consisted  of  the  stop- 
page of  a  ball  of  fire  less  than  a  yard  in  diameter,  while  to 
the  other  it  would  be  the  stoppage  of  an  orb  fourteen  hun- 
dred thousand  times  the  earth  in  size.  And,  even  accept- 
ing the  interpretation  which  instructed  divines  now  put 
upon  this  text,  that  Joshua  dealt  with  what  was  apparent 
merely,  but  that  what  really  occurred  was  the  suspension 
of  the  earth's  rotation,  I  think  a  greater  reserve  in  accept- 
ing the  miracle,  and  a  right  to  demand  stronger  evidence 
in  support  of  it,  will  be  conceded  to  a  modern  man  of  sci- 
ence than  would  have  sufficed  for  an  ancient  Jew. 

There  is  a  scientific  imagination  as  well  as  an  historic 
imagination,  and  when,  by  the  exercise  of  the  former,  the 
stoppage  of  the  earth's  rotation  is  clearly  realized,  the 
event  assumes  proportions  so  vast  in  comparison  with  the 
result  to  be  obtained  by  it  that  belief  reels  under  the  reflec- 
tion. The  energy  here  involved  is  equal  to  that  of  six  trill- 
ions of  horses  working  for  the  whole  of  the  time  employed 
by  Joshua  in  the  destruction  of  his  foes.  The  amount  of 
power  thus  expended  would  be  sufficient  to  supply  every 
individual  of  an  army  a  thousand  times  the  strength  of  that 
of  Joshua,  with  a  thousand  times  the  fighting-power  of 
each  of  Joshua's  soldiers,  not  for  the  few  hours  necessary  to 
the  extinction  of  a  handful  of  Amorites,  but  for  millions 
of  years.  All  this  wonder  is  silently  passed  over  by  the 


420  FRAGMENTS  OF  SCIENCE. 

sacred  historian,  confessedly  because  he  knew  nothing 
about  it.  Whether,  therefore,  we  consider  the  miracle  as 
purely  evidential,  or  as  a  practical  means  of  vengeance,  the 
same  lavish  squandering  of  energy  stares  the  scientific  man 
in  the  face.  If  evidential,  the  energy  was  wasted,  because 
the  Israelites  knew  nothing  of  its  amount ;  if  simply  de- 
structive, then  the  ratio  of  the  quantity  lost  to  that  em- 
ployed may  be  inferred  from  the  foregoing  figures. 

To  other  miracles  similar  remarks  apply.  Transferring 
thought  from  our  little  sand-grain  of  an  earth  to  the  im- 
measurable heavens,  where  countless  worlds,  with  their 
freights  of  life,  probably  revolve  unseen,  the  very  suns  which 
warm  them  being  barely  seen  by  us  across  abysmal  space  ; 
reflecting  that  beyond  these  sparks  of  solar  fire  suns  innu- 
merable may  lie,  whose  light  can  never  stir  the  optic  nerve 
at  all ;  and,  bringing  this  conception  face  to  face  with  the 
idea  that  the  Builder  and  Sustainer  of  it  all  should  contract 
himself  to  a  burning  bush,  or  behave  in  other  familiar  ways 
ascribed  to  him — it  is  easy  to  understand  how  astounding 
the  incongruity  must  appear  to  the  scientific  man.  Did 
this  credulous  prattle  of  the  ancients  about  miracles  stand 
alone ;  were  it  not  locally  associated  with  wrords  of  imper- 
ishable wisdom,  and  with  examples  of  moral  grandeur  un- 
matched elsewhere  in  the  history  of  the  human  race,  both 
the  miracles  and  their  "  evidences  "  would  have  long  since 
ceased  to  be  the  transmitted  inheritance  of  intelligent  men. 
Under  the  pressure  of  the  awe  which  this  universe  inspires, 
well  may  we  exclaim  in  David's  spirit,  if  not  in  David's 
words:  "When  I  consider  the  heavens  the  work  of  thy 
fingers,  the  moon,  and  the  stars,  which  thou  hast  ordained ; 
what  is  man  that  thou  shouldst  be  mindful  of  him,  or  the 
son  of  man  that  thou  shouldst  so  regard  him  ?  " 

If  you  ask  me  who  is  to  limit  the  outgoings  of  Al- 
mighty power,  my  answer  is,  not  I.  If  you  should  urge 
that  if  the  Builder  and  the  Maker  of  this  universe  chose  to 


REMARKS  ON  MIRACLES.  421 

stop  the  rotation  of  the  earth,  or  to  take  the  form  of  a 
burning  bush,  there  is  nothing  to  prevent  him  from  doing 
so,  I  am  not  prepared  to  contradict  you.  I  neither  agree 
with  you  nor  differ  from  you,  for  it  is  a  subject  of  which  I 
know  nothing.  But  I  observe  that  in  such  questions  re- 
garding Almighty  power,  your  inquiries  relate,  not  to  that 
power  as  it  is  actually  displayed  in  the  universe,  but  to  the 
power  of  your  own  imagination.  Your  question  is,  not  has 
the  Omnipotent  done  so  and  so  ?  or  is  it  in  the  least  likely 
that  the  Omnipotent  should  do  so  and  so  ?  but,  is  my  imagi- 
nation competent  to  picture  a  being  able  and  willing  to  do 
so  and  so  ?  I  am  not  prepared  to  deny  your  competence. 
To  the  human  mind  belongs  the  faculty  of  enlarging  and 
diminishing,  of  distorting  and  combining  indefinitely  the 
objects  revealed  by  the  senses,  or  by  its  own  consciousness. 
It  can  imagine  a  mouse  as  large  as  an  elephant,  an  elephant 
as  large  as  a  mountain,  and  a  mountain  as  high  as  the  stars. 
It  can  separate  congruities  and  unite  incongruities.  We 
see  a  fish  and  we  see  a  woman ;  we  can  drop  one  half  of 
each,  and  unite  in  idea  the  other  two  halves  to  a  mermaid. 
We  see  a  horse  and  we  see  a  man ;  we  are  able  to  drop  one 
half  of  each,  and  unite  the  other  two  halves  to  a  centaur. 
Thus  also  the  pictorial  representations  of  the  Deity,  the 
bodies  and  wings  of  cherubs  and  seraphs,  the  hoofs,  horns, 
and  tail  of  the  Evil  One,  the  joys  of  the  blessed,  and  the 
torments  of  the  damned,  have  been  elaborated  from  mate- 
rials furnished  to  the  imagination  by  the  senses.  And  it 
behooves  you  and  me  to  take  care  that  our  notions  of  the 
Power  which  rules  the  universe  are  not  mere  fanciful  or  ig- 
norant enlargements  of  human  power.  The  capabilities  of 
what  you  call  your  reason  are  not  denied.  By  the  exercise 
of  the  power  here  adverted  to,  and  which  may  be  called 
the  mytJiologic  imagination,  you  can  picture  to  yourself  a 
being  able  and  willing  to  do  any  and  every  conceivable 
thing.  You  are  right  in  saying  that  in  opposition  to  this 


422  FRAGMENTS  OF  SCIENCE. 

power  science  is  of  no  avail.  Mr.  Mozley  would  call  it 
"  a  weapon  of  air."  The  man  of  science,  however,  while 
accepting  the  figure,  would  probably  reverse  its  parts, 
thinking  that  it  is  not  science  which  is  here  the  thing  of 
air,  but  the  unsubstantial  figment  of  the  imagination  to 
which  its  solidity  is  opposed. 


THE   END. 


WOEKS  OF  HEEBEET  SPENCEE, 

PUBLISHED    BY 

E>.    APPLETOIST    AND    COMPANY. 


SYSTEM  OF  PHILOSOPHY 

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(New  and  Enlarged  Edition.) 
PART  I. — THE  UNKNOWABLE. 
PART  IL— LAWS  OF  THE  KNOWABLE. 

669  pages.    Price, $2.50 

IL— THE  PRINCIPLES  OF  BIOLOGY.— YOL.  I. 
PART  I. — THE  DATA  OP  BIOLOGY. 
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PART  III. — THE  EVOLUTION  OP  LIFE. 

475  pages.    Price,  - $2.60 

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PART  V. — PHYSIOLOGICAL  DEVELOPMENT. 
PART  VI. — LAWS  OF  MULTIPLICATION. 

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THE  OBIGm  OF  CIVILIZATION; 

OR,  THE 

PRIMITIVE  CONDITION  OF  MAN. 
By  SIR    JOHN   LTTBBOCK,  Bart.,  M,  P.,  F.  E.  S, 

3SO    rages.    Illustrated.. 

This  interesting  work  is  the  fruit  of  many  years'  research 
by  an  accomplished  naturalist,  and  one  well  trained  in  mod- 
ern scientific  methods,  into  the  mental,  moral,  and  social  con- 
dition of  the  lowest  savage  races.  The  want  of  a  work  of 
this  kind  had  long  been  felt,  and,  as  scientific  methods  are 
being  more  and  more  applied  to  questions  of  humanity,  there 
has  been  increasing  need  of  a  careful  and  authentic  work  de- 
scribing the  conditions  of  those  tribes  of  men  who  are  lowest 
in  the  scale  of  development. 

"  This  interesting  work — for  it  is  intensely  so  in  its  aim,  scope,  and  the 
ability  of  its  author — treats  of  what  the  scientists  denominate  anthropology, 
or  the  natural  history  of  the  human  species ;  the  complete  science  of  man, 
body  and  soul,  including  sex,  temperament,  race,  civilization,  etc." — Provi- 
dence Press. 

"A  work  which  is  most  comprehensive  in  its  aim,  and  most  admirable  in 
its  execution.  The  patience  and  judgment  bestowed  on  the  book  are  every, 
where  apparent ;  the  mere  list  of  authorities  quoted  giving  evidence  of  wide 
and  impartial  reading.  The  work,  indeed,  is  not  only  a  valuable  one  on  ac- 
count of  the  opinions  it  expresses,  but  it  is  also  most  serviceable  as  a  book 
of  reference.  It  offers  an  able  and  exhaustive  table  of  a  vast  array  of  facts, 
which  no  single  student  could  well  obtain  for  himself,  and  it  has  not  been 
made  the  vehicle  for  any  special  pleading  on  the  part  of  the  author." — 
London  Athenceum. 

"  The  book  is  no  cursory  and  superficial  review ;  it  goes  to  the  very  heart 
of  the  subject,  and  embodies  the  results  of  all  the  later  investigations.  It  ia 
replete  with  curious  and  quaint  information  presented  in  a  compact,  luminous, 
and  entertaining  form." — Albany  Evening  Journal. 

"  The  treatment  of  the  subject  is  eminently  practical,  dealing  more  with 
fact  than  theory,  or  perhaps  it  will  be  more  just  to  say,  dealing  only  with 
theory  amply  sustained  by  fact." — Detroit  Free  Press. 

"  This  interesting  and  valuable  volume  illustrates,  to  some  extent,  the 
way  in  which  the  modern  scientific  spirit  manages  to  extract  a  considerable 
treasure  from  the  chaff  and  refuse  neglected  or  thrown  aside  by  former  in 
quirers." — London  Saturday  Review. 

D,  APPLETON  &  CO.,  Publishers. 


D.  Appleton  &  Company^  Publications. 


LAY   SERMONS, 
ADD11ESSES,    AND    KEYIEWS, 

BY   THOMAS  HENRY  HUXLEY. 
Cloth,  12mo.      390  pages*      Price,  $1.75 

THIS  is  the  latest  and  most  popular  of  the  works  of  this  in- 
trepid and  accomplished  English  thinker.  The  American  edition 
of  the  work  is  the  latest,  and  contains,  in  addition  to  the  English 
edition,  Professor  Huxley's  recent  masterly  address  on  "  Spon- 
taneous Generation,"  delivered  before  the  British  Association  for 
the  Advancement  of  Science,  of  which  he  was  president. 
The  following  is  from  an  able  article  in  the  Independent : 

The  "  Lay  Sermons,  Addresses,  and  Reviews  "  is  a  book  to  be  read 
by  every  one  who  would  keep  up  with  the  advance  of  truth — as  well  by 
those  who  are  hostile  as  those  who  are  friendly  to  his  conclusions.  In 
it,  scientific  and  philosophical  topics  are  handled  with  consummate  abil- 
ity. It  is  remarkable  for  purity  of  style  and  power  of  expression.  No- 
where, in  any  modern  work,  is  the  advancement  of  the  pursuit  of  that 
natural  knowledge,  which  is  of  vital  importance  to  bodily  and  mental 
well-being,  so  ably  handled. 

Professor  Huxley  is  undoubtedly  the  representative  scientific  man  of 
the  age.  His  reverence  for  the  right  and  devotion  to  truth  have  estab- 
lished his  leadership  of  modern  scientific  thought.  He  leads  the  beliefs 
and  aspirations  of  the  increasingly  powerful  body  of  the  younger  men  of 
science.  His  ability  for  research  is  marvellous.  There  is  possible  no  more 
equipoise  of  judgment  than  that  to  which  he  brings  the  phenomena  of 
Nature.  Besides,  he  is  not  a  mere  scientist.  His  is  a  popularized  phi- 
losophy  ;  social  questions  have  been  treated  by  his  pen  in  a  manner  most 
masterly.  In  his  popular  addresses,  embracing  the  widest  range  of  top- 
ics, he  treads  on  ground  with  which  he  seems  thoroughly  familiar. 

There  are  those  who  hold  the  name  of  Professor  Huxley  as  synony- 
mous with  irreverence  and  atheism.  Plato's  was  so  held,  and  Galileo's, 
and  Descartes's,  and  Newton's,  and  Faraday?g.  There  can  be  no  greater 
mistake.  No  man  has  greater  reverence  for  the  Bible  than  Huxley.  No 
one  more  acquaintance  with  the  text  of  Scripture.  He  believes  there  is 
definite  government  of  the  universe ;  that  pleasures  and  pains  are  distrib- 
uted in  accordance  with  law ;  and  that  the  certain  proportion  of  evil 
woven  up  in  the  life  even  of  worms  will  help  the  man  vho  thinks  to  bear 
his  own  share  with  courage. 

In  the  estimate  of  Professor  Huxley's  future  influence  upon  science, 
his  youth  and  health  form  a  large  element.  He  has  just  passed  his  forty- 
fifth  year.  If  God  spare  his  life,  truth  can  hardly  fail  to  be  the  gainer 
from  a  mind  that  is  stored  with  knowledge  of  the  laws  of  the  Creator's 
operations,  and  that  has  learned  to  love  all  beauty  and  hate  &&  nleness  of 
Nature  and  art. 


SPENCERS  SYSTEM  OF  PHILOSOPHY. 

THE  PHILOSOPHY  OF  EVOLUTION. 

By  HERBERT  SPENCER. 


This  great  system  of  scientific  thought,  the  most  original  and  important  men- 
tal undertaking  of  the  age,  to  which  Mr.  Spencer  has  devoted  his  life,  is  now  well 
advanced,  the  published  volumes  being:  First  Principles^  The  Principles  of  Bi- 
ology, two  volumes,  and  The  Principles  of  Psychology,  vol.  i.,  which  will  bo 
shortly  printed. 

This  philosophical  system  differs  from  all  its  predecessors  in  being  solidly 
based  on  the  sciences  of  observation  and  induction ;  in  representing  the  order 
and  course  of  Nature ;  in  bringing  Nature  and  man,  life,  mind,  and  society,  under 
one  great  law  of  action ;  and  in  developing  a  method  of  thought  which  may  serve 
for  practical  guidance  in  dealing  with  the  affairs  of  life.  That  Mr.  Spencer  is  the 
man  for  this  great  work  will  be  evident  from  the  following  statements : 

"  The  only  complete  and  systematic  statement  of  the  doctrine  of  Evolution 
with  which  I  am  acquainted  is  that  contained  in  Mr.  Herbert  Spencer's  '  System 
of  Philosophy ; '  a  work  which  should  be  carefully  studied  by  all  who  desire  to 
know  whither  scientific  thought  is  tending."— T.  H.  HUXLEY. 

"  Of  all  our  thinkers,  he  is  the  one  who  has  formed  to  himself  the  largest  new 
scheme  of  a  systematic  philosophy." — Prof.  MASSON. 

"If  any  individual  influence  is  visibly  encroaching  on  Mills  in  this  country,  it 
is  bis."— Ibid. 

"  Mr.  Spencer  is  one  of  the  most  vigorous  as  well  as  boldest  thinkers  that 
English  speculation  has  yet  produced."— Jomr  STUART  MILL. 

"  One  of  the  acutest  metaphysicians  of  modern  times."— Ibid. 

"  One  of  our  deepest  thinkers."— Dr.  JOSEPH  D.  HOOKEB. 

It  is  questionable  if  any  thinker  of  finer  calibre  has  appeared  jji  our  coun- 
try."— QEOBGE  HENRY  LEWES. 

"He  alone,  of  all  British  thinkers,  has  organized  a  philosophy."— Ibid. 

"  He  is  as  keen  an  analyst  as  is  known  in  the  history  of  philosophy ;  I  do  not 
except  either  Aristotle  or  Kant."— GEORGE  RIFLE Y. 

"  If  we  were  to  give  our  own  judgment,  we  should  say  that,  since  Newton, 
there  has  not  in  England  been  a  philosopher  of  more  remarkable  speculative  and 
•ystematizing  talent  than  (in  spite  of  some  errors  and  some  narrowness)  Mr.  Her- 
bert  Spencer." — Londor*  Saturday  Review. 

"  We  cannot  refrain  from  offering  our  tribute  of  respect  to  one  who,  whether 
for  the  extent  of  his  positive  knowledge,  or  for  the  profundity  of  his  speculative 
insight,  has  already  achieved  a  name  second  to  none  in  the  whole  range  of  Eng- 
lish philosophy,  and  whose  works  will  worthily  sustain  the  credit  of  EnglUk 
thought  in  the  present  generation."—  Westminster  Beview. 


D.  APPLETO&  &  CO.'S  PUBLICATIONS. 


ON 

THE  ORIGIN  OF   SPECIES 

BY 

Means  of  Natural  Selection ; 

OR, 

THE  PRESERVATION  OF  FAVORED  RACES 

IN   TUB 

STRUGGLE  FOE  LIFE. 

BY 

ID-A.IVWXN',    .A..  M. 

One  Volume.    12mo.    Cloth.  $2.00. 


"  His  first  point  is  to  show  that  species  are  in  many  cases  not  well 
defined,  and  that  the  whole  order  of  natural  history  seems  to  be  in  a 
state  of  mutation,  by  reason  of  constant  variations.  Thus  even  under 
domestication,  important  changes  may  be  introduced  by  intercrossing, 
by  selection  of  the  best  individuals  for  propagation,  by  crossing  parents 
marked  by  however  slight,  but  favorable  peculiarities. 

"His  second  point  is  what  he  terms  the  universal  and  necessary 
struggle  for  existence.  This  follows  from  the  high  geometrical  ratio 
of  increase  common  to  all  beings.  If  there  were  no  catastrophes, 
any  one  of  the  existing  species  would  be  sufficiently  numerous  in  a 
few  thousand  years  to  cover  the  whole  earth,  to  the  exclusion  of  every- 
thing else. 

"  His  third  point  is  to  prove  that  this  struggle  is  directed  by  the 
law  of  natural  selection.  Even  the  races  of  domestic  animals  may  be 
constantly  improved  and  modified  by  choosing  the  best  individuals 
for  propagation.  Nature  brings  the  same  discipline  to  bear  upon  the 
whole  domain  of  animal  and  vegetable  life.  She  seizes  at  once  upon 
any  slight  variation  that  is  favorable,  and  perpetuates  it ;  in  the  uni- 
versal pressure,  any  variation  that  is  injurious  is  immediately  extin- 
guished." 


THE  DESCENT  OF  MAN, 


AND 


SELECTION  IN  RELATION  TO  SEX. 


BY 


CHAS.  PAR  WIN,  M.  A.,  F,  E.  S, 

Two  Vols.,  12mo. 


PRICE,     .....    $4.00 


In  these  volumes  Mr.  Darwin  has  brought  forward  all  the  facts  and 
arguments  which  science  has  to  offer  in  favor  of  the  doctrine  that  man 
has  arisen  by  gradual  development  from  the  lowest  point  of  animal  life. 
He  had  originally  intended  this  work  as  a  posthumous  publication,  but 
the  extensive  acceptance  of  the  views  unfolded  in  his  book  on  the  "  Origin 
of  Species  "  induced  him  to  believe  that  the  public  were  ripe  for  the  most 
advanced  deductions  from  his  theory  of  "Natural  Selection."  Aside  from 
the  logical  purpose  which  Mr.  Darwin  had  in  view,  his  work  is  an  original 
and  fascinating  contribution  to  the  most  interesting  portion  of  natural 

history.  

From  the  London  Spectator, 

"For  our  part,  we  find  Dr.  Darwin's  vindication  of  the  origin  of  man  a  far  more 
wonderful  vindication  of  Theism  than  Paley's  '  Natural  Theology,'  though  we  do 
not  know,  so  reticent  is  his  style,  whether  or  not  he  conceives  it  himself/' 
From  the  Citizen  and  Round  Table. 

"  Even  the  charge  of  atheism,  which  was  so  violently  urged  against  Mr.  Dar- 
win, is  now  rarely  heard,  and  theologians,  whose  orthodoxy  is  unquestioned,  have 
ventured  to  admit  that  it  is  possible  to  believe  both  in  Christianity  and  the  Dar- 
winian theory  at  the  same  time." 

From  the  Charleston  Courier. 

"No  one  can  rise  from  an  ordinarily  attentive  consideration  of  Mr.  Darwin's 
treatise,  without  being  impressed,  not  only'  with  the  extent  and  depth  of  the 
knowledge  which  he  has  attained  upon  the  subject  under  treatment,  and  his  long, 
unwearied  labor  in  collecting  facts,  but  also  with  his  possession  of  qualities 
equally  rare— the  true  scientific  temper,  the  transparent  candor,  and  the  truth- 
seeking  soberness,  with  which  he  expresses  to  you  his  conclusions,  and  the  pro- 
cesses oy  which  he  reaches  them. 

"  Whether  you  like  his  discourse  or  not— though  you  may  refuse  to  acquiesce 
in  his  conclusions— still  you  are  compelled  to  bear  your  witness,  that  this  man 
has  not  been  laboring  to  find  facts  to  support  a  preconceived  theory,  but  that  the 
theory  is  the  irrepressible  outgrowth  of  his  accumulated  facts." 
From  the  Evening  Bulletin. 

"  This  theory  is  now  indorsed  by  many  eminent  scientists,  who  at  first  com- 
bated it,  including  Sir  Charles  Lyell,  probably  the  most  learned  of  living  geolo- 
gists, and  even  by  a  class  of  Christian  divines  like  Dr.  McCosh,  who  think  that 
certain  theories  of  cosmogony,  like  the  nebular  hypothesis  and  the  law  of  evolu- 
tion, may  be  accepted  without  doing  violence  to  faith." 

Sent  free,  by  mail,  to  any  address  in  the  U.  S.,  on  receipt  of  the  price. 

D.  APPLETON  &  CO.,  Publishers. 


Works  published  by  D.  Appleton  db  Co. 


HEAT, 

CONSIDERED  AS  A  MODE  OF  MOTION, 

Being  a  Course  of  Twelve  Lectures   delivered    before  the 
Royal  Institution  of  Great  Britain. 

BY  JOHtf  TTODALL,  F.  K.  8., 

reoFESSOB  or  NJLTTTBA.I,  PHILOSOPHY  IN  THE  EOYAI.  INSTITUTION— AUTHOK  yr  nu 
"GLAOTEBS  OF  THE  ALPS,"  ETC. 

With  One  Hundred  Illustrations.     Svo,  480  pages.    Price,  $2. 


Prom  the  American  Journal  of  Science.— With  all  the  skill  which  has 
made  Faraday  the  master  of  experimental  science  in  Great  Britain,  Professor  Tyndall 
enjoys  the  advantage  of  a  superior  general  culture,  and  is  thus  enabled  to  set  forth  his 
philosophy  with  all  the  graces  of  eloquence  and  the  finish  of  superior  diction.  "With  a 
simplicity,  and  absence  of  technicalities,  which  render  his  explanations  lucid  to  un- 
scientific minds,  and  at  the  same  time  a  thoroughness  and  originality  by  which  he  in- 
structs the  most  learned,  he  unfolds  all  the  modern  philosophy  of  heat.  His  work  takes 
rank  at  once  as  a  classic  upon  the  subject 

KTew  York  Times. — Professor  Tyndall's  course  of  lectures  on  heat  is  one  of  the 
most  beautiful  illustrations  of  a  mode  of  handling  scientific  subjects,  which  is  com- 
paratively new,  and  which  promises  the  best  results,  both  to  science  and  to  literature 
generally ;  we  mean  tile  treatment  of  subjects  in  a  style  at  once  profound  and  popu- 
lar. The  title  of  Professor  Tyndall's  work  indicates  the  theory  of  heat  held  by  him, 
and  indeed  the  only  one  now  held  by  scientific  men — it  is  a  mode  of  motion. 

Boston  Journal.— He  exhibits  the  curious  and  beautiful  workings  of  nature  iu 
ft  most  delightful  manner.  Before  the  reader  particles  of  water  lock  themselves  or  fly 
asunder  with  a  movement  regulated  like  a  dance.  They  form  themselves  into  liquid 
flowers  with  fine  serrated  petals,  or  into  rosettes  of  frozen  gauze ;  they  bound  upward 
in  boiling  fountains,  or  creep  slowly  onward  in  stupendous  glaciers.  Flames  burst  into 
music  and  sing,  or  cease  to  sing,  as  the  experimenter  pleases,  and  metals  paint  them- 
selves upon  a  screen  in  dazzling  hues  as  the  painter  touches  his  canvas. 

New  York  Tribune. — The  most  original  and  important  contribution  that  has 
yet  been  made  to  the  theory  and  literature  of  thermotics. 

Scientific  American.— The  work  is  written  in  a  charming  style,  and  is  the 
most  valuable  contribution  to  scientific  literature  that  has  been  published  in  many 
years.  It  is  the  most  popular  exposition  of  the  dynamical  theory  of  heat  that  has  yet 
appeared.  The  old  material  theory  of  heat  may  be  said  to  be  defunct. 

Louisville  Democrat.— This  is  one  of  the  most  delightful  scientific  works  w« 
hsTe  ever  met.  The  lectures  are  so  full  of  life  and  spirit  that  we  can  almost  imagine 
the  lecturer  before  us,  and  see  his  brilliant  experiments  in  every  stage  of  their  progress. 
lli«  theory  is  so  carefully  and  thoroughly  explained  that  no  one  can  fail  to  understand 
tt.  Such  books  as  these  create  a  love  for  science. 

Independent.— Professor  Tyndairs  expositions  and  experiments  are  remarkably 
thoughtful,  ingenious,  clear,  and  convincing;  portions  of  the  book  have  almost  tb« 
interest  of  a  romance,  so  startling  are  the  descriptions  and  elucidations. 


Wwks  of  Herbert  Spencer  published  by  D.  Appielon  &  C*. 
A  NEW  SYSTEM  OF  PHILOSOPHY. 

FIRST   PRINCIPLES. 

&  VoL    Large  12mo.    515  Pages.    Price  $2  50. 

CONTENTS : 
PAKT  FIRST.— The  Unknowable. 

Ciiaptei  i.  Religion  and  Science;  IL  Ultimate  Religious  Ideas;  IIL 
Ultimate  Scientific  Ideas ;  IV.  The  Relativity  of  all  Knowledge ;  V  Th« 
Reconciliation. 

PART  SECOND.—  Laws  of  the  Knowable. 

I.  Laws  in  General;  IL  The  Law  of  Evolution;  IIL  The  same  con- 
tinued; IV.  The  Causes  of  Evolution;  V.  Space,  Tune,  Matter,  Motion,  and 
Force ;  VL  The  Indestructibility  of  Matter ;  VII.  The  Continuity  of  Motion ; 
VIIL  The  Persistence  of  Force ;  IX.  The  Correlation  and  Equivalence  of 
Forces;  X.  The  Direction  of  Motion ;  XI.  The  Rhythm  of  Motion;  XII.  The 
Conditions  Essential  to  Evolution ;  XIII.  The  Instability  of  the  Homoge- 
neous ;  XIV.  The  Multiplication  of  Effects ;  XV.  Differentiation  «*nd  Inte- 
gration ;  XVI.  Equilibration ;  XVII.  Summary  and  Conclusion. 

In  the  first  part  of  this  work  Mr.  Spencer  defines  the  province,  limits,  and 
relations  of  religion  and  science,  and  determines  the  legitimate  scope  of 
philosophy. 

In  part  second  he  unfolds  those  fundamental  principles  which  have  been 
arrived  at  within  the  sphere  of  the  knowable ;  which  are  true  of  all  orders 
of  phenonema,  and  thus  constitute  the  foundation  of  all  philosophy.  The 
law  of  Evolution,  Mr.  Spencer  maintains  to  be  universal,  and  he  has  here 
worked  it  out  as  the  basis  of  his  system. 

These  First  Principles  are  the  foundation  of  a  system  of  Philosophy 
bolder,  more  elaborate,  and  comprehensive  perhaps,  than  any  other  which 
na*  been  hitherto  designed  in  England. — British  Quarterly  Review. 

A  work  lofty  in  aim  and  remarkable  hi  execution. — Cornhill  Mayadnt. 

In  the  works  of  Herbert  Spencer  we  have  the  rudiments  of  a  positive 
Theology,  and  an  immense  step  toward  the  perfection  of  the  science  of  Psy- 
chology.—  Christian  Examiner. 

If  we  mistake  not,  m  spite  of  the  very  negative  character  of  his  own  ro- 
Kilts,  he  has  foreshadowed  some  strong  arguments  for  tlte  doctrine  of  a  post 
tire  Christian  Theology. — New  Englander. 

As  far  as  tte  frontiers  of  knowledge,  where  the  intellect  may  go,  there  ft 
to  living  man  whose  guidance  may  more  safely  be  trusted.— 


Work*  <tf  Herbert  Spencer  published  by  D.  AppUtcn  &  Co. 
Tiie  Fhilosopliy  of  Herbert  Spencer. 


THE 

PRINCIPLES    OF   BIOLOGY 

Vol.  I.    475  pages.    (Now  in  press.) 

CONTENTS: 
PART  I. — THE  DATA  OP  BIOLOGY. 

L  Organic  Matter. — II.  The  actions  of  Forces  on  Organic  Matter. — III.  The 
re-actions  of  Organic  Matter  on  Forces. — IV.  Proximate  Definition  of 
Life. — V.  The  Correspondence  between  Life  and  its  Circumstances.— 

VI.  The  Degree  of  Life  varies  as  the  Degree  of  Correspondence.— 

VII.  The  Scope  of  Biology. 

PART  II. — THE  INDUCTIONS  OF  BIOLOGY. 

L  Growth. — II.  Development. — III.  Function. — IV.  Waste  and  Repair. — 
V.  Adaptation.— VI.  Individuality.— VII.  Genesis.— VIII.  Heredity.— 

IX.  Variation.— X.  Genesis,  Heredity,  and  Variation.— XI.  Classifica- 
tion.— XII.  Distribution. 

PART  III. — THE  EVOLUTION  OP  Luna. 

I.  Preliminary. — II.  General  Aspects  of  the  Special-creation-hypothesis. — 
III.  General  Aspects  of  the  Evolution-hypothesis. — IV.  The  Arguments 
from  Classification. — V.  The  Arguments  from  Embryology. — VI.  The 
Arguments  from  Morphology. — VII.  The  Arguments  from  Distribution. 
— VIII.  How  is  Organic  Evolution  caused  ? — IX.  External  Factors. — 

X.  Internal  Factors. — XI.  Direct  Equilibration. — XII.  Indirect  Equili 
bration. — XIII.  The  Cooperation  of  the  Factors. — XIV.  The  Converg 
ence  of  the  Evidences. 


All  these  works  are  rich  In  materials  for  forming  intelligent  opinions,  even  where 
we  are  unable  to  agree  with  those  put  forth  by  the  author.  Much  may  be  learned  from 
Jhcm  in  departments  in  which  our  common  Educational  system  is  very  deficient.  The 
active  citizen  may  derive  from  them  accurate  systematized  information  concerning  hia 
highest  duties  to  society,  and  the  principles  on  which  they  arc  based.  He  may  gaio 
dearer  notions  of  the  value  and  bearing  of  evidence,  and  be  better  able  to  distinguish 
between  facts  and  inferences.  He  may  find  common  things  suggestive  of  wiser  thought 
—nay,  we  will  venture  to  say  of  truer  emotion— than  before.  By  giving  us  fuller  rcali- 
tations  of  liberty  and  justice  his  vritings  will  tend  to  increase  onr  self-reliance  in  the 
ireat  emergency  of  civilization  to  which  we  have  been  summoned Atlantic  Monthly 


D.  APPLETON  &  CO.'JS  PUBLICATIONS. 
THE 

Correlation  and  Conservation  of  Forces. 

WITH  AN 

. NTBODUCTION    AND    BKIEF    BIOGEAPHICAL   NOTIOES 
By  EDWARD  L.  YOUMANS,  M.D.     12rao,  490  pages. 

CONTENTS. 

L  By  W.  R.  GROVE.    The  Correlation  of  Physical  Forces. 
IL  By  Prof.  HELMHOLTZ.    The  Interaction  of  Natural  Forces. 
HI.  By  J.  R.  MATER.     1.  Remarks  on  the  Forces  of  Inorganic  Nature. 

2.  On  Celestial  Dynamics. 

3.  On  the  Mechanical  Equivalent  of  Her  t. 

IV.  By  Dr.  FARADAY.    Some  Thoughts  on  the  Conservation  of  Forces. 
V.  By  Prof.  LIEBIO.     The  Connection  and  Equivalence  of  Forces. 
VI.  By  Dr.  CARPENTER.    The  Correlation  of  the  Physical  and  Vital  Forces 

"This  work  is  a  very  welcome  addition  to  our  scientific  literature,  and  will  be 
particularly  acceptable  to  those  who  wish  to  obtain  a  popular,  but  at  the  same  time 
precise  and  clear  view  of  what  Faraday  justly  calls  the  highest  law  in  physical  science, 
the  principle  of  the  conservation  offeree.  Sufficient  attention  has  not  been  paid  to  the 
publication  of  collected  monographs  or  memoirs  upon  special  subjects.  Dr.  Youmans' 
work  exhibits  the  value  of  such  collections  in  a  very  striking  manne%  and  we  earnestly 
hope  his  excellent  example  may  be  followed  in  other  branches  of  science."— American 
Journal  of  Science. 

"  It  was  a  happy  thought  which  suggested  the  publication  of  this  volume.  The 
question  is  often  asked,  and  not  so  easily  answered,  What  are  the  new  doctrines  of  the 
Correlation  and  Conservation  of  Forces?  In  this  volume  we  have  the  answer,  and 
with  the  reasons  of  its  chief  expounders ;  those  who  are  ignorant  on  that  theme,  can 
thus  question  the  original  authorities." — Neio  Englander. 

"We  here  have  the  original  expositions  of  the  new  Philosophy  of  Forces,  accompa- 
nied by  an  excellent  exposition  of  both  the  expositions  and  the  expositors;  the  whole 
will  be  a  rare  treat  to  the  lovers  of  advancing  scientific  thought."— Methodist 
Quarterly  Review. 

"  This  is,  perhaps,  the  most  remarkable  book  of  the  age.  We  have  here  the  latest 
discoveries,  and  the  highest  results  of  thought  concerning  the  nature,  laws,  and  con- 
Bections  of  the  forces  of  the  universe.  No  higher  or  more  sublime  problem  can  engage 
the  intellect  of  man  than  is  discussed  by  these  doctors  of  science  intent  alone  on  aniv 
tog  at  the  truth."— Detroit  Free  Press. 

'This  work  presents  a  praiseworthy  specimen  of  complete  and  faithful  authorship, 
•ad  it*  publication  at  this  time  will  form  an  epoch  in  th«  experience  of  many  thinking 
mind  a." —  ibune. 


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